1) There's quite a few different options in regards to muzzle devices you could opt for. It all depends on what kind of performance you want out of them; flash suppression, recoil compensation, and/or braking muzzle rise. It also largely depends on how much you're willing to spend. I'm a big fan of the PWS FSC47
for 7.62x39 AK's with 14x1 LH threading, though some people refuse to pay that much for a muzzle device for their AK.
2) In regards to front sight posts, anything you get that has a tritium bar or some kind of mark on it is going to be good for close aiming, but not that great for any kind of distance aiming. On the other side of the spectrum, any kind of thin or fine front sight post will be great for distances but not very quick for close stuff. You could probably try using your original sight post and use a bright paint marker to mark a thin part of the the top of it or you could try something like this