I've lost a lot of weight and my only exercise has been walking. most of the weight lost has come from the areas involved in walking- thighs, calves buttocks and belly. from the abdo down things are looking pretty good. Not much weight gone from the ribs up tho- back,shoulders,arms and boobs and i want to change this and do more work on the abdomen flab.

I have a couple of problems though. I had a stroke several years ago and although I made an excellent recovery it left me with some left sided weakness. I noticed on my legs that I've gained more muscle on the right so made an effort to lead from the left which is helping even them out nicely.
1) But when I do sit-ups I'm very aware most of the effort is from the right sided muscles and my left side is kind of free-loading. push ups are kind of the same. I'm going to look really weird I think if I persist like this so I need advice
2) I need basic exercises for the upper body and arms and was thinking of weights but don't know where to start here. I was thinking of getting those weighted arm band things to start with so that all the time those muscles are working a bit more. I was also looking into kettlebells but I'm in unexplored territory so I need advice here too
please bear in mind I'm the athletic equivalent of a slug