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.