This is actually quite simple.
Step one - use PVC electrical conduit, not PVC pipe.
Step two - provide an access point (such as an LB, or a junction box) for every 360 degrees (at most) of turn. This will be something that remains accessible by removing a panel when the walls are closed back up, like any other junction box access.
If you have 6 90 degree turns, either put in 3 90's and an access point (if using an LB, that can be the access point) or 4 90's an an access point, depending how the run works out best for placing the access point. Use electrical conduit sweeps, not plumbing 90's or 45's.
3, access point, 3 would be most balanced, but
4, access point, 2 is also fine.
There's no need to get too excited about leaving a pull string in place - you can always vacuum one in, or pull one in while pulling an old cable out. Do it, or don't do it, as you prefer. Do make sure that the ends of your conduit terminate in junction boxes from which the cables leave by fairly tight holes or grooves (or through proper cable clamps, but that can be tricky with pre-terminated cables), so that your conduit does not become your new rodent pathway and nest.
Seems like a shoddily built roof. So, I think the roof will fail long before painted walls will cause a problem.
It sounds like the outside paint is already 'breathable' if it's absorbing water and capillary action is bring it to the inside. As such, I'd argue that waterproofing the interior is a good thing. Keep the moisture in the wall and allow it to dry to the outside.
Best Answer
Elevating the conduit 7/8” or more off the roof surface will be more effective than painting but yes white is the least heat absorbing color. Why 7/8” elevation? That is what code requires or a temperature adder is used when derating the wire; with 7/8” elevation, the adder is not required. This is located in section 310.15(A)(3)(c), "Raceways and Cables Exposed to Sunlight on Rooftops".