I agree that it takes some time for these guys to really put on weight. I wouldn't expect more than 0.1g per month. Some of these guys will start at a really high hatch weight and then lose a little. Plus, these guys are so small, it really makes a difference on when you weigh them. If they have just defecated, that's probably 0.1g there.
I think there is a point to where they will start gaining weight quickly. I wouldn't really expect a rapid weight gain until they are past the 3-5 month period.
You can feed them as much as they will eat, but I think you'll find that they really only want to eat EOD at best. I've simply found that mine won't really eat more than 3 times a week (especially if I'm doing roaches, they tend to like crickets a lot better). What I've actually been doing is gradually increasing the prey size rather than number of items. I pick each cricket or roach out by hand (tweezer).
I weighed one of each of my three hatched clutches. The oldest is 4 months 1.89g, the next is 3 months 1.68g.. the last is almost 2 months 1.58g (this scale is to the 0.0000).