A bi-fold Dahon/Tern (and all the various good quality clones like Fnhon, Rifle, Crius, etc) will be good enough.

As for upgrades.
1. Assuming the bike comes with a 9speed RD, then add a cheap FD and fd-shifter and the chainring to a 2x; worth considering will be to swap out the usual stock square taper BB while changing the crank.


Thats about it actually.
A bike as such has high utility and is inexpensive.
Spend the rest of the money on bags that mount on the bike and a rear rack.

I just built another such bike for my son for a trip at the end of the year. (Will share some photos when I have the chance to take some)