For city driving, I don't hot dog it with the gearshifts. Usually 2500 or 3000 is a nice shift point. There's only 4 gears so you don't need to do much shifting.
Out of the city, with longer stretches of roads, I frequently go a little above that. You have to in order to keep up with the traffic.
If I goose it, I think just after 5000 is a nice shift point in first and second gear. After that I just shift to 3rd then 4th, because I don't like to go much faster than 60mph. I can, and have once or twice, but it's just not fun after that. For me I enjoy lower end speeds. Cruising speed is 35-40 for me. The car is very happy and tame at that speed.
Plus, I really do enjoy the initial take off. I enjoy listening to the gear changes and the revs. There's a little sweet spot at 3000 in my car where the exhaust sounds so amazing. It's just a great sound to hear with the top down.
As far as handling, I've found that your same basic RWD guidelines are applicable. I've found that the handling is pretty forgiving for a RWD car (more than an S2000, 325Ci BMW, many other RWD's), but that it still is RWD (remember, RWD rewards expertise but punishes the lack of it). You can jostle them around pretty good and they will, for the most part, stay on dry road like a roller coaster. Just learn to carry the weight of the car through turns properly---don't upset the weight balance of the car. Don't be taking turns at 45 miles per hour and jamming on the brakes half way through. Although these are things you should follow in any RWD car! I know the limits of the late model B fairly well and I caught on well. They are easy cars to drive and you will fall in love with the cornering. One of my favorite things is the rack and pinion steering---I feel EVERYTHING and the car is almost an extension of my own self when I drive it. But above all, I'm never TOO confident of the car.
The one thing about an MG that you might want to know, that I found out, is this. Coming from driving a modern car for a few years with super powerful brakes and ABS, you do have to brake differently with an MGB. I have power brakes on my car, but it does brake differently than my 2001 3 series. You have to brake sooner. So if you are used to a car with ABS and super good brakes, then maybe take a day or so JUST getting used to braking.
Too bad we have things like shock rebound and weight, and our cars aren't go karts :(
Good luck!!! :):)