Goldfish do eat some live plants. But I dont know which ones.

It's largely impossible to keep any plants with goldfish except for those with either thick and waxy leaves or those that taste bad for the fish

MB Gold covered the two kinds, I've got them in my tank in various sizes and they make for a really nice aquascape!
It's also, as she says, very important to quarantine everything you put into the tank, plants and fish may carry parasites or other unwanted horrors, so keep it separated for at least three weeks. If the plants have parasites, it's enough to keep them in a quarantine tank with a bit raised temperature and the parasites would die.

It might be too late for him I don't know, I can't tell. And it's always pretty hard to notice if your fish are uncomfortable before it's too late! Especially when it hasn't really happened before so you'd recognize the signs

Wish there was something like that here!
However, I buy my plants from a smaller more aquarium-themed pet shop (my favorite!) and I usually don't quarantine those plants since the fish kept with them are always healthy, not once have I seen a sick or dead fish in the tanks there And I've been buying the plants from those tanks for more than a year now, without quarantine and no problems!
It'd still feel better if the plants were packaged separately so that I'd be sure that there wouldn't be anything unwanted on them.

What type of snails are you likely to find on plants?

Caffuss you may be thinking of the Bladder Snails

I have also heard of people finding Ramshorn snails and Malaysian Trumpet Snails, but I'm sure other kinds could turn up every now and then