First off.......nice work you are doing, looks good, well thought out.
Finishing with a file is a good method, lots of powered sanding process leaves flat spots..
No (very few) shortcuts for true highend results.
Your front fender brace, I cant picture over the top looking good except maybe if its also a brace. A slightly easier way if I may suggest.. Look at the stock type, make cereal box template of one half of it, and get it so it looks near right. Then cut two pieces (.070-.090 thou), stack and build together, both at once. (a good trick is to drill either in center of big hole or corners, then drive 1/8" roll pin thru). Then when forming the curve under fender it may be easier and quicker.
When done, you may or may not weld middle together.
Reason for going underneath, if something gets in there, it wont tear fender off as easily. You need some clearance... Many guys rode over a beer or soda can with an evil grin and lost their fender..plus fall over...
Good luck with it all...remember a Cameo from a dealership roaming the streets here when I was a young kid..