[kuoka]

First of all... Welcome!

To answer your questions...

1. 80 is fine and even if it dips below or goes a bit high, as long as the temp change isn't drastic, you should be fine.
2. LR placement is a lot of personal preference. It can rest against the tank IMO but I'd leave clearance so you can get a mag cleaner between it and the wall. I also prefer to put small base rock under my LR to maximize flow under the rock as well.
3. The plastic hydrometer's aren't as accurate as "refractometers" but do the job in the beginning. (refractometers are expensive). I'd "calibrate" your plastic one by marking where your water reports then take a sample to your LFS where they can test it or against another sample with a refractometer (make sure the refractometer is properly calibrated.
4. Wait until everything stabilizes IMO. If you want to add corals closely after cycling, I'd go with something hardy like zoas, frog spawn, etc.
5. Tank janitors are cleaners for the tank. They consist of snails, hermit crabs, etc. to eat detritus or other wastes in the tank. You'll get other hitch hikers with your LR that will help too.
6. Go hardy at first... leather corals, monitpora, frog spawn, zoas, short tentacle plates, etc. IMO
7. There are a lot of beginner sites for reefers on the www (google them). RC has some good links too.

Don't worry about the brown algae. It's diatoms and are normal during cycling and will go away on its own almost as fast as it appeared. You might also get slime algae and green hair algae.. these too are normal during cycling.

Ps. I like the aquascape. Good luck!