Admittedly I am mostly just going with what I know... I haven't actually taken the ferry before. I'm not sure I'd want to risk it right now, though.

If you decide to go to Cherrygrove, you should be able to stay at their Pokémon Center for free, at least for a few days. There isn't much to do or see in Cherrygrove, so most people don't stick around there for that long.