Buy a good U-lock, and leave it in the parking garage if you can get away with it. Tell a security guard or lot attendant what you plan to do, and why- they shouldn;t have a problem with it. It'll save you carrying the extra weight 22 miles a day. Lock your bike somewhere that gets a fair amount of foot traffic, so that hopefully someone would see a would-be thief messing with it. Bottom line though is that if someone wants your bike, they'll probably take it. Is your parking garage mostly just for an office building? If it's the kind of place where most of the people through it are there day in day out, you might feel a little safer than if there's retail mixed in and you might see more passing-thru opportunity type thieves. Lock it through the front wheel and frame to something solid. A cable lock through the back wheel might be helpful as well.
Lightwise- spend what you think is worth spending. Anything below $20 is probably gonna disappoint. Last winter I used a $40 Cateye in conjunction with a $15 Trek up front, and I'm looking to replace those with something more substantial this year. Lots of rear blinkies help too. One or more on your bike, one on your bag, and maybe your helmet. This year I think I'm gonna go with one on my bag, one on my chainstays, and get a set of those Knog lights that replace your bar end caps.
I'm in the DC area as well, and my commute is rsing from 6.5mi each way to about 11 or 12, starting next week, also mostly on an MUP. Good luck- I'll probably see you out there someday.