What are standard design rules for a Flex Printed Circuit (FPC)?
There are no standard design rules, each manufacturer, unfortunately, has their own design rules.  These are dictated by how tightly controlled they run their processes.  Even if they use the same machines and processes it will vary a little.  Vias in FPC (which are small) are not an issue unless you expect to flex the cable lots and PTH parts should be fine as well as long the parts are mounted (the body supplies some rigidity).  SMT devices can be an issue as the rigid body combined with flexing generates large stresses on the pads and can pull the pads off.

Have run PTH, SMT and wire bonds onto FPC and rather than use rigid flex (which is a good option) we used FR-4 (and some times ceramic) stiffeners on the backside to prevent flexing in that region (no traces, just ).