As for the first part, I get that. Killing one mob and gaining there abilities is kind of too easy. I get that. But killing any more than 10 or so would start to get tedious and boring.as being the person who suggested this... by killing more mobs to gain more abilities from that mob would make you spend more time on that mod in progressing it. now I'm not saying that tedium is the best choice for balance, but just 1 kill is really not alot to gain everything right of the bat.
as for the inventory limit, I myself was thinking along the line of having a block in that limited inventory that you could place down, then you can stand on it and morph back into yourself, then do the things you need to do and morph back into a bat.
As for the latter, why not just morph back and forth? I mean, there's a few seconds between forms so it really doesn't matter. I just don't see a point in limiting what you can wear or use in certain forms since people will just morph out of them.