In my games, both so far, it's surprisingly been KH who are the powerhouse who steamroller Makedonia. They've already taken Korinthos and have tried Demetrias several times. I don't think I helped by raiding Pella in the first turn and destroying all the military buildings there (including naval yards and blacksmiths). So Rhodos might be a no-brainer then. They won't defend it well, and as you say it'll refocus their attention on the Greek mainland. That might be enough to tip the balance back towards stalemate, plus Rhodos is rich.

Perhaps Mytilene would be a good target after Rhodos?

Ptolemies are winning against the Seleukids and are presently my allies. But perhaps as you say Cyprus is another island steal worth taking a risk over.

Pontos and the Seleukids aren't long off warring over Mazaka, though Pontos aren't very powerful right now.