But can answer some of your other needs.
Most of Center City south of Market Street to South Street, and between the rivers is a pleasant walking neighborhood. My favorite places to walk are on Delancy Place/Street between 15th & 22nd, anywhere in Old City (anywhere south of Chestnut on the streets with numbers lower then 8th), and on South Street between 2nd & 7th (although weekends there get really hairy with all the mobs of kids)
As for live music, I've heard good things about
The World Cafe Live in West Philadelphia (the area around Drexel and Penn), where you'll also find many of the ethnic restaurants.
You may want to browse some issues of
The City Paper and
Philadelphia Weekly to get a non-tourists feel for the city. Both have run articles about specific neighborhoods, and both advertise a LOT of live music.
I'm probably not the person to show you the ropes, since 1) I only work in the city (live in the 'burbs) and 2) -- I'm afraid to admit this on DU -- I don't like live music and my only ethnic restaurant experiences are in Chinatown and the many Italian places all over the city.
Also, don't assume this weather as the norm. July & August are the worst times to be here - the natives usually head to the South Jersey or Delaware shore to get away from The Soup.