Fish tank questions.

Ok so I have a few questions that I've been reminded of after doing a part water change and was wondering whether anyone could help? First off, I have three large stones in my tank, whats the best way to clean them? As they are starting to go green, and although the fish eat bits off it every now and again, Gary stays on the glass mostly, and I would like them to be a bit cleaner at least, on that note how big do most snails grow? As Gary seems bigger by the day. Also is there anywhere online that sells cheap but realistic looking plastic plants? Just so that when the fish have destroyed a real one my tank doesn't look empty until I get back into town? Also when I buy a real plant would it survive in a plastic goldfish bowl, thats unused, but so I could keep a eye out for snails before placing it into the tank, as I'll prob miss any small snails or eggs, as I'm well me , and if so how long does it take for snail eggs to hatch?

I never clean my stones on the bottom or the rocks in my tank - don't want to waste all that god bacteria!

Are the rocks touching the sides of the tank so Gary could get on them?

No there in the middle, never thought of that lol, will move everything around as I picked out the remains of a plant today, so it could do with a make over.

Do you have a light on in the tank, if so, how long is the light on for per day?
Where is the tank situated? middle of room? near a window?

Its in the far corner of the room, but does get sunlight in the evenings, the lights on from when I wake up, till around 8 in the evening, so between 12-14 hours.