Bro,

For the rims, its just a question of performance over comfort. Bigger rims mean better handling, smaller ones less 'tagtag' hence more comfort. Choose one 1st then settle for the aesthetic considerations as to what type you like (ie wide lips, chrome, gun metals, 5 spoke 6 spoke etc and those sort of stuff)

As for mufflers, there are several shops that can actually do acceptable mods like mufflerland. I had mine done sa mga kanto kanto lang along Kamuning. The cost is cheaper but the quality (and I just started to learn from it) is quite dubious. Jasma muffs are good according to feedback. Pretty pricey though.

For IHE mods, there are a lot of inputs from enthusiasts from the club I'm a member in (Nissanbayan) Since you own a nissan (I own one too :-) I suggest you join the club. A lot of really really nice inputs there from fellow Nissan owners.

Hope these help.