Thanks, everybody, for your words of support. I really appreciate it! I'm really, really working on not stressing myself and keeping things in perspective. It's not the end of the world. It's just toys.
There are two issues to accepting money from users to upgrade the server capability:
1) Entering the grey area of a commercial site. There seems to be a tacit agreement with Playmobil at the moment, that they won't prosecute me for copyright infringement; but once money starts to change hands, they may have no choice but to involve the lawyers. Nobody wants that.
2) Once I accept payment for service, even donations or advertising, I have an obligation to provide something to the users, an obligation I don't have now. It's a hobby and that's all. I can quit the whole thing if I want to. I don't want to, but you never know what's down the road! I cannot handle a new "real" job.
I can't imagine I could generate enough income from this to replace my day job or even to support some time off to devote to it, so unless there was a steady stream sufficient to pay for a dedicated server - 10 to 15 times what I pay now - it would just be a little bonus really, and once it was set up, if the income decreased, I'd feel pressured to pay for any shortfall. Not to mention, the time it has always taken day-to-day wouldn't change much... and the data store is only increasing in size. What happens when the new server runs out of capability? I'm thinking of the future, too.
On the good side, Playmobil has said, "let's talk". I won't go into details until I actually have something concrete to report, but I'm hopeful.