Five miles is a really short commute; looking for side, peripheral and parallel streets might add a couple or three miles, but if you don't want to ride on the busy streets, it's worth it, and your commute will still be easily doable. But have you actually tried riding on the streets you are talking about? If you aren't used to riding in traffic at all--and it sounds like you aren't if you're looking for sidewalks to ride on--it can be scary and intimidating at first, but if you do it, it gets easier and you will become much more confident.

My approach, though, would be to look for an alternate route; I know in my city it's not always possible, but most of the time it is, and I regularly go out of my way to ride on quieter, less-trafficked streets.

Also, I think you can have a bike that is both a pleasure to ride but also not so attractive to thieves; I ride a "vintage" bike that most thieves wouldn't bother with if there was something newer and prettier parked next to it--and there always is--but I keep it in excellent running shape, and that's the key.

"Beater" doesn't have to be synonymous with "ugly, decrepit piece of crap that is no fun to ride."