I'm certainly no Beijing expert, but here's what I suggest ...
Kind of all depends on your budget, of course, but for nice bars, restaurants and boutique-type shops I'd head to South Luogu Lane (not far from Houhai lake, which is also pretty good for bars, and there's an amazing jazz bar on the shore of the lake too, but its name escapes me ...).
If you're able to, then it's probably a good idea to stay somewhere around the Forbidden City area of town, as then you're not really too far in a taxi from a lot of the good spots to visit, eat and drink.
For the wall, I'd suggest Simatai. It's about a 3 hr mini-bus ride away (which you can organise through any number of hotels in the city): amazingly picturesque and, because of the journey, not too crowded ...
Hope this helps!