Examples of some COH charactes of mine done in CO (and a couple of others)

[Sofaspud]

In short, no -- you keep everything if you fall back to Silver status.  You just can't use the gold-level shinies (and have to convert whatever characters you want to play, to Silver, before playing them).

Details from here: http://www.champions-online-wiki.com/wiki/F2P_FAQ

EDIT: Oh, something else I discovered.  If you're working on a new character costume, hit the Save button before you tell it to go ahead and create the character.  Because CO is fond of logging you off due to inactivity while you're messing about with costumes, which means all that work you did tweaking it magically vanishes on you.

--sofaspud
--"Listening to your kid is the audio equivalent of a Salvador Dali painting, Spud." --OpMegs