1. Unless it's a VERY casual wedding, e-vites are tacky. Also consider that not all your guests may regularly use e-mail, or computers, and so may miss the invitation or not know how to reply.
2. Where I'm from, a cash bar is the definition of tacky. If you can't afford alcohol, then you just don't serve any, or have a wine and beer bar only. It might be different where you live.
3. A nice thought if the particular women would enjoy it: not everyone does.
4. It always looks cheap, and requires a guest to manage it. DJs are professionals, so they have access to everything, know what songs to play when, how to get the crowd going, etc. For me, they add a lot to the party.
5. Personally, I didn't expect my MOH to do anything except pick out and buy her dress, and show up. It's my wedding, so I planned it, made decisions, ran the errands, etc. As long as you're not asking too much of them, I would think they'd understand that the MOH simply can't do the things you've asked them to do because she's not there.