I've gotten to the point where I can farm Act 2 easily and starting to get bored of it. The first part of Act 3 is easy as long as I don't get surrounded, but after Ghom everything pretty much kills me fast. I have close to 20m to spend but I am not sure where I can get the greatest improvement for the gold.
Yes, my resists are a little low relative to my other stats. I have a little bit of MF but could always use more.. That will come later I guess. I would rather kill stuff faster with no MF, than kill slower with lots of MF. That's how I rolled in D2 as well and did just fine.
I'd say from here you should look to boost your resistances by 100 or so, like liquid_mage said, and also add in Life Regeneration or Life Steal. You could get those mods on your jewelry, maybe, and more resists on your shoulders.
The only weakness is your build and gear, I think, is that Revenge is your only way to gain back life (unless you're using the Life Steal rune on Ignore Pain). So I'd definitely focus on that, even if it's at the expense of a little bit of Strength.