Okay, here's how it works.
For each 200 reputation points you get, you got +1 of ''rep power''
Meaning.
0 rep = +1
200 rep = +2
400 rep = +3
600 rep = +4
It won't go higher than 4 rep for normal users.
(Users with negative rep (red gem) gives 0 rep. You must be neutral or have positive rep to give +1)
Then for moderators, they can give from +12 to -12, including 0.
Admins can give how much they want.
For the post count thingy, it's every 2500 posts, your rep power is supposed to increase, but it's not true as ''Just_spectating'' has 5000+ posts and gives only 2 rep (he has about 370 rep).
I hope it answers you, every 200 rep and it doesn't matter how many posts you have.