How do I tell if studs are even?

HI; I think I got myself really confused because we started talking about patching, and this grew into a plastering project for me. The areas that were low from the removed plaster, like the ceiling, I just filled back up with Kal-Kote all in one coat, so that was between 3/8" and 1/2" of plaster all at once. Now I am starting to think that plastering is all suppose to be done in thin layers between 1/16" and 1/8", even in conventional plaster systems. Is this correct? So did I really mess up filling in those huge thick areas with Kal-Kote all at once? Is there any worry of it having poor integrity due yo my heavy fill? In the areas with the heavy fill, the edges have turned white, but the center where it is the heaviest has stayed darker and looks more like it did when it was wet, but it is all very hard. So even when patching, do I want to keep with thin even coats as much as possiable? Thanks Jamie p.s. I think my keens wall may have dried out without setting, it is still not hard, 36 hours after I applied it. It is showing a few small hair line cracks in the surface, but not many. I am wondering if it will ever get strong enough or if I should scrape now.

I plan on a 2' x 2' suspended ceiling in my finished basement. I've found the traditional metal grid (Armstrong), a plastic suspended grid ([URL="http://www.acpideas.com/index.cfm?XlinkID=15"]ACP HG Grid[/URL]) and the flush systems ([URL="http://www.acpideas.com/index.cfm?XlinkID=13"]ACP Gridmax[/URL] or [URL="http://www.kensa.com/"]Ceiling Link[/URL])that surface mount to the rafters. Head room isn't an issue for my basement, so loosing a few inches for the suspended ones isn't a big deal, although it would make trimming out the windows easier. On the other hand, my wall system has some upper brackets that won't be completely hidden if I use the flush mount. Crown molding would cover that though, but might look goofy with the drop ceiling. Aside from that, are there any down sides or up sides to the vinyl vs. the metal? I haven't done a cost analysis yet, but I assume the vinyl is cheaper. I'm going to have can light in the ceiling, does that rule out the vinyl? Any experience at all would be helpful.