Agree with Mike, and I'll try to hit some highlights on your questions. Thanks for numbering them, and as always... many of these things are "just my opinion"!!
1. "Live" rock and sand just means it's "live" with beneficial bacteria. No way of knowing which is which. After a month or so, it will all be "live."
2. Yes... you can keep arranging the rock until you like it, and yes, it will stress things out a little. So try and do as much planning beforehand and keep the hands in the tank to a minimum. But definitely arrange things to your liking. Only way not to squish things is... well... just don't squish them!
3. Securing rock is a huge topic. Do some searching here and you'll find lots of info. You can use plastic zip ties, aquarium safe epoxy, or even drill the rock and insert acrylic rods between pieces. Lots of ways to do it.
4. I vacuum the top 1/2" or so of my sand. Don't stir it.
5. Yes... you have FAR too many fish, and fish that shouldn't be housed long term in a 10g tank. Only thing I'd even consider housing long-term in a 10g would be a clown goby, or fish like that. A 10g quarantine tank is good for clowns, etc... but long term... not good.
6. Tank is way overcrowded as it is, and is probably headed for some rough times in the future if it stays that way. I wouldn't add anything, if it was me, before reducing the bioload and understanding the ins and outs of keeping a marine aquarium.
7. Can't help ya there... but even with an upgraded light, keeping stable water parameters in a 10g is a tough thing. Especially if you're just starting out. And anemones need good, stable water.
8. Best thing is to use rubber/latex gloves when handling corals. Some can sting and leave welts, some don't. And some folks are more sensitive than others. Corals like zoanthids contain a potent neurotoxin in their mucous. Best bet is to just use gloves and error on the side of caution.
9. See #6, and yes... I wouldn't even consider a star in anything under 75g.
10. See #6. And I wouldn't even consider cucumbers. Beautiful things, but if they get overly stressed or die, they pretty much nuke your tank.
11. Nothing really you can do anyway, so just keep an eye on it. Sometimes it takes a while for them to acclimate to their new surroundings. Sometimes they lose their crown (the "feathers") due to the stress of the move and it will take a while for it to grow back. Only time will tell.
12. Probably better to use your hands since you can be gentler.
13. The snails will do fine. If you've overstocked on snails, some will die off and you will have some natural population control going on.
14. Can't say for sure without knowing what kind it is. But for the most part, there should be a knob or dial somewhere on it that you can turn to adjust the thermostat setting - assuming it is adjustable. Rule #1 is don't trust a thermostat on a heater... they are notoriously incorrect. Best thing is to get a separate thermometer (I like the small digital Coralife ones) and adjust your thermostat based on the thermometer. It's not unusual to have your thermostat set at 78 and see your thermometer read 76.
15. If you're not going to add anything (see #6!), no need for a quarantine tank. Until something gets sick. Quarantine tanks can be run all the time, or set up only when needed. If set up when needed, you need to be prepared with something to provide biological filtration in the newly setup tank - or spend the time to re-cycle the quarantine tank.
The best advice for you right now is to stop, not add anything to this tank, and research what it is you want to take back to the LFS
. Keeping all the stuff you have in a 10g is just a disaster waiting to happen. It could take a week, or a month, but it will happen unless you devote every waking second to this tank. I would not trust any LFS
that sells a 10g tank to a beginner, and lets them stock it the way you have. Not your fault... you were just given some bad advice.
Welcome aboard, keep asking questions, and in the mean time you might want to get a hold of a book by Robert Fenner called "The Conscientious Marine Aquarist". It's an absolute must-read for anyone starting out in this hobby.