I don't think we need a lookout. Usopp is good enough for the job since he actually does it all the time. And he has a sharp eye being the gunner and all so I don't think they'll need someone who specializes in looking.

A shipwright is a downright necessity.

Is a helmsman a stern handler? If it is then that would be good. Seeing as when there are storms or strong current it seems that they need more than one person cause its so hard to move it. Someone who specializes in that area would be a good addition.

Luffy HAS to get a musician. Nuff said.

I also don't want just fighters joining luffy's crew. Like I said before. I always liked the combo of his crew. They all have an important job but at the same time they are freakishly strong fighters.

So including the captain, that makes the last 3 members with jobs that might join luffy's crew to complete the 10 members he originally wanted.