The brown stuff is called diatom, and is a algae that often shows up when you are mostly through the initial cycle. So the answer is yes, it does help indicate you are ready to go to the next step. However, since you added 4 fish, you will have to endure another spike, as the bacteria that process the ammonia and nitrite are not sufficient to take that bioload as well. Nothing can be done about that now, so you will just have to do lots of water changes until your bacteria load increases enough to support what you have in the tank.
There is a pretty prolific debate on the need for skimmers. Most say yes, some say no. Basically, they help a lot in maintaining water quality. If you can squeeze 6 or 8 inches between the tank and wall, you can get a decent HOB
fixture, or plumb in a sump with a weir/overflow system. Here is a site that has some great info on how a sump system works. http://www.melevsreef.com/
That might solve your space issue!
Sounds like you are well on your way! Hope things continue to go well for you.