It can be fuselage mounted provided the fuselage is thin enough where you mount it.

It does not need to be in line with the carb but I would not deviate too far. How far did you have in mind?

Yes, you can defuel through the fueler as it will be drawing through the clunk. Check the fueler filter for contamination on a scheduled basis. Once a month should do IMHO.

Mounting the fueler on the cowl, when you press in the fueler probe it may cause the cowl to flex and eventually crack. I would not put any more holes in the cowl than you need to.