I've never done that trip inbed79, but last year we got the ferry from Kos to Bodrum and we didnt need a visa.

You do need to take your passport though.

Your visa is valid for 90 days so you don't need to get a new one.

never done that trip but had a day in Rhodes town when we was on a cruise and I must say it was a wonderfull place..
great for shopping and a magnificent castle..

we did the rhodes trip when we were in marmaris. had a great day out, really enjoyed it, especially the old town
we booked the trip with our tour operater {probably paid through the nose) but lots of places selling the trip in marmaris itself
we didnt have to pay for a visa on return to marmaris

Rhodes Catamaran is running in May but not everyday. when u bought ur ticket from travel agents its including pick up/drop back, port tax and insurance.

Rhodes town is a great place for a visit.
We did Bodrum to Kos Town and it was quite straightforward