I don't think selling a solo-FC without a housing plot attached to it for gil is against the ToS. Just remember that if you plan to transfer, there's only so much gil you can take with you when you do. I know there's been talk about removing the gil limit for transfers to certain servers, but that hasn't been confirmed that it will definitely be implemented yet. So that's something to think about.

You can only take a maximum of 1,000,000 gil with you on your person, and 800,000 gil per retainer, when you transfer.