Somehow in the course of writing this, it became a rather large wall of text:
Well, I'm blind myself, so I do know what I'm talking about here--not that others don't, but getting answers from the sighted only goes so far. The answers here are quite good and I agree with almost everything, but blindness really does have to be experienced. Two disclaimers; I've never released anything and I do have a bit of vision. I am completely color-blind (so far as I'm aware I see the world in grayscale).
As a blind person, there's no reason to be afraid of descriptions. You can, truthfully, write them as well if not better than anyone else. If you play muds for a while before trying to write your own, you'll know what colors things typically are and what adjectives typically go with them. I don't know, for instance, what exactly a tiger looks like, but I like to read so I know what tigers are associated with; I know that green is generally something applied to plants, red typically to blood, and the like. I know that a fearsome tiger is a perfectly reasonable description, as is green foliage with pointed leaves. Most muds don't even go that far, nowadays. As for things like fireballs and dragons and the like: it's fantasy. Is it blue with purple dots? I doubt the player will much care, so long as you're not too over the top; there've been dragons with fur, and perhaps your fireball spell is globes of burning oil. The best approach is to try to describe things in terms of other things, not to try to describe them in terms of themselves--that's easier said than done, and you have to be careful not to use too many similes. For the most part, knowing that something is burning is enough; as soon as you try to describe exactly what the flames are, you begin to lose your audience. Want to evoke violence? "The carpet is the crimson of blood." Want to evoke growth? "The green of grass" or perhaps "The clean, fresh air."
The vaguer you let something be while still describing it, and you have to be talented enough to pull this off, the more real it can seem (I've seen this in a few places--I'm not able to do it, few are). Essentially, everyone sees everything differently--to you, grass isn't green plants; it's something that crackles, probably, or something that feels a certain way on your feet.
Descriptions are something everyone finds difficult, including myself, and you're not the only one who can't write them--I don't believe, however, that this is a function of blindness; I think instead that it's a function of life experience and writing talent. Some people can write a book; that doesn't mean I can, even though I like to read them.
I tried, once, to get a project with lpc going. It didn't end well, because I didn't like most of the mechanics from everything. If you don't like most of the preexisting mudlibs at all, do be aware that it's sometimes easier to build new systems than tear them out--if you want to redefine magic and combat and the like, you may be better off starting with something lacking those features. I'd look around and see what is available that's more minimalistic. That said, everything you mentioned in your first post as wanting to do should be doable with, for example, dead souls which is just about as far from minimalistic as it's possible to get. It really comes down to how much you want to change from the default mudlib and how good at coding you are.
If you're not dead set on lpc, and I know this is blasphemy on these boards, you could go learn something like java. I'd only do this, though, if you want to do something *really* different. All of my project ideas were that way, and I eventually decided that, if I was going to write a mudlib from scratch, I'd do it in a language that I can go get a job with. I'm in college for a computer science major, however, so making it a marketable skill is more important to me. By something really different I mean quite literally dropping the idea of a room to some extent. I will say this though: learning a new programming language while trying to start from nothing on a mud (You don't even have a room until you write it, and you're going to end up writing the network code too, so you can't even connect) is like jumping into the deep end of a pool when you don't know how to swim; you might learn to swim, but you're probably going to sink. I didn't learn programming on a mud and, in fact, when I taught myself programming I hadn't even heard of them.
You already know tads, so you do know a "real" programming language. It's for a specific domain, but a lot of the knowledge will transfer to lpc; you can probably transfer half of it to java and a third of it to c++ (java is much, much simpler than c++).
As for your actual question, should you start your own or join one, I'd also say join one.
To everyone else:
Firstly, a mud client for the blind is much more than just connecting a voice. In general, it calls into the screen reader directly via apis that the screen reader exposes. The screen reader already provides a voice configured to the user's preferences and a way to get at that voice; I, for one, wouldn't want to have two text to speech voices going at once. What exactly a screen reader is and how it's different from just a text-to-speech voice probably deserves a post of it's own. I will say this, though, I've never heard of a blind person using ZMud. Generally, it's mushclient with one of the screen reader plugins that are floating around or, more recently, vipmud a non-free client written specifically for the blind (and with which I have many, many problems given that I can get mushclient to do more with the same level of accessibility and without paying $30). For anyone who might read this and is looking for a mud client for the blind, if you have any computer skill beyond the basics, go look up mush-z or one of the mushclient tts plugins; mushclient does more and, in fact, you could almost write a mud or webserver on top of it (this would be a hack to rule all hacks, don't actually try). And, people can actually help you do things. Again, this probably deserves a thread if there's enough interest.
As for descriptions. I can only speak for myself, but I do read them and I do appreciate well-done ones. But, I don't read them again, and if your mud doesn't let me turn them off while leaving enough useable navigational information in a non-spammy format, I'm gone. Generally, I turn brief on, and it better provide some sort of exit list, and type look for the full description when the short description interests me. The issue here isn't that I can't appreciate them, it's that I can't skip them without skipping other stuff--as text comes in, it's put into a buffer of things to be said; I can stop the speech by emptying that buffer, but I then have to go back and manually check everything I just skipped. Others may read them more or less than I with varieing levels of enjoyment etc.
I would say that, for the blind, it has to do with life experience. I got into books about 4 years back and, now, am running out of things I want to read simply because I've read most of the good stuff that everyone reccomends; I now spend entire afternoons looking for new books to read, simply because all the lists I find list exclusively things I've already read. This gives me a good working knowledge-base of things that I can't see; I don't know exactly what they look like, but I have enough information to, for example, solve a quest. My reading habbits are primarily fantasy, so that helps even moreso with the mudding descriptions.
And, I'll never admit it to them, but my parents also had a lot to do with this. From a very, very young age, they would go out of their way to get me first-hand experience. I've been in a real plane cockpit (before 9/11, obviously), felt a possum, the list goes on forever; I can't remember most of it simply because that kind of thing was so common in my childhood. I'm not saying the op didn't have these kind of experiences, just trying to answer the question of how I see the world. My small bit of vision helps, of course, but most of the things are "Like an x but without y"; as my list of x without y grows, so does my understanding of the world because each "x without y" combination becomes another x. I probably see the world way, way differently than most people, simply because some level of distortion does occur when you only have descriptions, but I have a model and can enjoy/write a description for a mud based off that model, and you can't tell that my model is different.
Firstly, end wall of text. Secondly, I really need to add this forum to my list of forums to check on.