At the beginning of the story luffy stated that he wants to have 10 crew
members, that means that there should be a total of 11 strawhat-pirates.
Currently we have 9 with luffy, that means there should be 2 more.
(it could also be more, but I don't think so because it was a very obvious hint from oda)
I think that luffy will gather his crew very soon because they're about to enter the new world and the crew should share the most of the experiences as a complete pirate group.
I mean it would be very dumb if the last crew mate enters 2 or 3 arcs before the end.
So let's see what we already have:
- Captain - Luffy
- First Mate - Zoro
- Sniper - Usopp
- Chef - Sanji
- Navigator - Nami
- Doctor - Chopper
- Archeologist - Robin
- Shipwright - Franky
- Musician - Brook
I personally think that they could need a helmsman (blackbeard has one too), but it wouldn't be necessary. At the moment I can't think of more.
Also what species would they be?
I hope one of them would be a fishman or a mermaid. I really like them, besides they could fill the job of the diver for underwater inspection (hey, just found another job). If it would be like this i think it would be the fishman because he also could walk on land like a human (I know that mermaid could do it too, but they have to be 30 years), they're generally stronger and it is a species that oda has invented himself (I'm sure he's proud of it^^).
(PS: If somebody doesn't understand my english, please excuse me and feel free to correct.)
(I know I use a lot of brackets )