Harajuku is a good place to go on a Sunday afternoon, but not as colorful as it once was.

Sunday is the only day off for a lot of people, so stores in general are open, including those in Akihabara.

All the places you mention are on the Yamanote Line (silver-colored JR trains with green stripes running in an amoeba-shaped loop), so you could easily manage all of them in 24 hours.

If you want maximum Shibuya, Saturday night is great. Find a hotel in Shibuya, but take the N'EX there and emerge into chaos. You will find every kind of restaurant, from high-end to low-end, and youth-oriented bars and clubs, many of them tucked away on side streets. I don't give restaurant recommendations, because I've always found great food simply by wandering around, checking out the posted picture menus and/or window displays, and sniffing the air.

I'm not a habituée of Roppongi, so I can't help you there, but in general, the high-end places on the Ginza are geared toward business people on expense accounts, the kinds of places where, if you have to ask the price, you can't afford it.

Shibuya will have good sushi and good everything else, as long as you know where to find out.

Ask someone at your hotel where to find the best sushi in the area, but let them know what your budget is first. I once arrived in Tokyo with a yearning for good tempura, and the hotel first steered me toward one of those places with no prices posted. When I explained that I was thinking of something more reasonable, they understood that I wanted to go to one of the restaurants where ordinary people eat.