Trust me on this one: get a folding bike. With the right model, you can take it inside with you anywhere, including the bars. Not only that, it can be a serious chick magnet.

By being able to bring the bike inside with you, you never have to worry about locking it up or what is attached to it. That is part of the reason why I found folding bikes, I got tired of buying ever-increasingly secure U locks and Kryptonite chains, and I got really, really tired of my my bikes getting scratched while in a bike rack.

I bought a Brompton H6L, which has full fenders, a rear rack of limited capacity, and a proprietary handlebar bag with decent capacity. I added front & rear lights, and I have never, ever locked it up once, because I have never left it outside unattended, despite the fact it is my most-ridden non-winter bike. If I go anywhere I think they may object to someone carrying a folded bike inside, I put the bike in a Bromptom B-bag, which folds up easily and can be toted while folded without much effort. 99% of the time, I just carry in the bike and it's not a problem, quite the opposite, in fact.

You don't have to get a Brompton, and if the ride is flat enough you don't need 6 gears, but if you are going to be carrying the bike up stairs or around people you'll definitely want something with 16 inch wheels (20 inch wheels or greater can be unwieldy). You may or may not want an aluminum frame, which of course is usually lighter than the steel frames. For what you're looking for, you'll definitely want something with a small fold, which by default means 16 inch wheels, and something with a proprietary bag to carry it in. With that, all of your other concerns are negated. You don't have to take any precautions against theft because the bike will never be exposed to thieves.