I put a slice of raw cucumber in the tank every week for the snails/ pleco. About an inch or so thick, and leave it until it's gone, which takes them somewhere around 3 days- you have to weigh it down to the bottom with something. A decorative rock & a rubberband work well. I have 4 snails and a 7" pleco in that tank right now, though (had 7 snails, at one point- inherited the pleco and moved some snails out so the pleco has a chance to eat)- you probably won't need that large of a piece of cucumber. Your goldies will probably also chew at it, and it is fine for them to eat, if they make head way with it. They will all enjoy some romaine lettuce, as well. Nope- that is not too hot for the snails. Your single tailed goldfish might think it's a little toasty, but, they are pretty adaptable. That is definitely at the high end of his recommended temp, though, and the snails and moor could go lower (I keep my fancy tank at 74-76, too... to my knowledge, single tailed varieties like lower). If it's just your room temp, don't worry about it... it isn't crazy high, or anything.
If you have a water softener, you will probably need to add calcium. If you get hard water stains and build up (in the shower, on sinks, etc) you probably won't need to. I am sure someone else who is a lot more knowledgeable with this part can tell you more of what you need to do, here.
If your snails do crawl out of the tank (which I have only seen with mine when one crawled up the tube leading to the spray bar from the canister filter to lay her eggs above my high water level- and only one time), they will not go far. Like, as in, it would be very rare for them to even leave the inside of the tank. About to the water line is as far as I have seen any of mine go, with the one exception of my one girl who wanted to lay eggs. (which apparently in the wild they lay eggs on tall reeds sticking out of the water- so, not too abnormal) So, no, you shouldn't expect to come home & see one crawling across the living room floor, or on the wall behind the tank, on the top of the tank or outside walls, or anything. They are capable of leaving the water for a little bit, but really prefer to stay in the water, from what I have seen.