Unless you want to use a fixie, srsly I'd use:
a modern 5 or 6 speed freewheel on the rear, which will allow a rear wheel with minimal dishing, 39/52 on the front, drop bars, steel frame, rack, guards and down tube shifters. It will let you use chains which will wear comparatively slowly, it will be low maintenance, and replacement drivetrain kit will be inexpensive. It is gonna be dirt cheap to get it together.
I think hardwearing derailleur multi speed will be the next fixed (i.e. the big thing in the bike market). At which point it will no longer be dirt cheap.