A couple of things:
First, get the book the Concientious Marine Aquarist by Fenner. It has TONS of info for beginners. I read it cover to cover. He talks about alot of the above issues.
It's an easy read and will get you started in the right way.
Skimmers--you will get alot of conflicting info, but if you have several fish, you should really think about having one. I noticed alot of difference in my tank after I put in a skimmer versus before the skimmer.
Beginner corals,--zoos, rics, mushrooms all are good. I do acclimate my corals to temp by floating the bag. I always acclimate my SPS, but they aren't exactly beginner corals. I used to drip my zoos, but several folks said don't do it.
Attaching mushrooms---robharold and Nate82 are dead on with what they said. Another method I use is to place the mushroom/ric on a piece of rubble/rock/frag plug etc in the position I want it. Then, place netting over the coral and the rock/rubble etc and tie the netting to itself (string/rubber band or some other reef safe material) so that the coral is lying directly on the rubble etc and can't float off. After a couple of weeks, the coral will have attached and you can remove the netting.
Hope this is helpful.