1. Blue line is very safe between ORD and downtown. In fact, the L in general is pretty safe for visitors.
2. Tough question. Both cities have so many variations that you will probably find similarities and differences at every place. If you want a good steak, and an authentic experience, I suggest Gene & Georgetti's. I've sent co-workers there and they've loved it. Otherwise, there are of course all the fancier places. Another unique Chicago steakhouse experience is Gibson's.
3. What are your interests? Also, I assume you're going soon, when it could still be cold. You're in a central location for all the museums, aquarium (which may be the best in the country), planetarium, Lincoln Park Zoo, the Hancock, Willis (Sears) Tower. If it's nice, rent one of the Divvy bikes and bike along the lake from your hotel up to Lincoln Park. For restaurants, go to the West Loop. Also, my #1 recommendation for visitors is to take the river architectural tour. There are a couple locations right around River North.
I and others will be happy to give recommendations if you can be a little more specific.