recommended resistances for maps?

Should I go over the 75% cap, or leave it and avoid elemental weakness maps and such?

If you're in HC, then overcap.... If you're in SC, then don't bother overcapping and ele weakness maps won't be that hard unless you're melee.

Perfect gear situation you want to have enough over the cap to be able to run resists maps + resists monsters within the map.

But realistically, most builds can run up to yellow maps without overcapping and still run any of those maps. Unless you run something like elemental weakness map + monsters deals 100% additional damage of 1-2 elements. Those are rippy.

Business class: overcapped
Reasonable: use a curse immune flask, sacrifice one aura for purity of elements to run ele weakness maps
Semi-yolo: compensate with endurance charges / flasks for ele weakness maps
Yolo: no curse immune flask, no overcapping, run ele weakness maps without extra effort (a.k.a. I don't want to level)

If you can overcap without compromising your damage or other defenses, it's surely worth it.

It's not absolutely necessary though, you can swap one of your auras for Purity of Elements or one of your gear pieces for one with better resists (but maybe worse other stats) to run Ele weakness maps.

For random curses in maps you should have at least a Utility flask of Warding anyways.

AFter the release of that new +35 to all resistances flask, I don't bother ele-weak capping anymore.

Just focus on getting res caps. If you play ele weakness maps, take that flask with you for the duration of the map.

The new utility flasks have actually help fill quite a bit of holes in some of my older builds that weren't balanced right (cause I sucked at builds when I was learning).

If you are playing HC, I would still try for the ele weakness cap...but it's not that easy to accomplish sometimes unless you want to use mainly rares and no uniques in your build.