3.) Not sure what you're asking. By artificial bottom do you mean the kind of turf mats sold at pet stores? That can be a little abrasive sometimes and there's a kind of fake moss with loops in it that I've heard of frogs getting their feet stuck in. Either way should generally be okay though.

4)It's natural but not necessarily healthy. Some frogs won't mate if they don't get to hibernate. But even in the wild, some frogs die during hibernation. I think some may even need to hibernate (Budgett's?) I don't know about Spring Peepers in particular but other tree frogs can live to a ripe old age without hibernating once.