1) You do not need a beta reader, several writers on here don't have one.
2) The finer points are up to you, but maybe the pokemon isn't used so much for battling as guiding? Maybe have the pokemon have all the other senses heightened since blind people often have the same thing. If you want to battle with it, have the trainer state the pokemon to turn to a certain direction, and then have the pokemon fire off a special attack or something. I've never thought about it before.
3) Serp Serperior?
4) Beta readers are actually not available at the moment. We used to have a beta reader thread, but that went inactive. There were also a huge number of writers with a small amount of beta readers, so that didn't help either. Hope I helped!
Beta readers are certainly not necessary, but they can help. So it's up to you. The thread we have here is inactive, but I suppose you can still post in it and if someone sees it that is interested in helping out, they can talk to you about it. Sometimes you can get feedback too in the Share Your Writing thread we have.
As for the blind Pokemon question - well, I suppose it depends on what you want to do with it. Battle? Just be a pet of sorts?
How it acts would in some way, I feel, be down to its species, and why/how it has no sight. A Pokemon like a Zubat, for instance, rely much more on sound than anything else. A dog Pokemon would rely more on smell. Meanwhile, if the Pokemon was always blind may differ to one that lost its sight from old age or an accident or something in how it acts. By considering the background of a Pokemon and asking questions, you may be able to build up how it would behave. The same for a trainer. Are they new to this, or experienced? Would they find this handicap too hard to manage? (That's a biggy - they don't have to manage, after all). And so forth.
Assuming that the blind Pokemon was one that relies heavily on its vision, keep in mind that the trainer would probably find it pretty awkward to battle with from the start, unless the trainer in question is very experienced and very sensitive. He/she would probably have to devote a lot of extra time to learning to coordinate the blind Pokemon, and so his other Pokemon would get less attention and level up slower.