<< So if I am working on a concept object that is 340cm in length. Should I be modeling it in 1/10th scale, so 34cm in length?

No just place middle of object at the origine with a raisonnable unity! cm is perfect in this case!
After it's depend of the total size of the project!

<<about Loft
If you rebuild the curve before Loft you will have a very regular curve with a minimum of Control points!