Taps to install, 2 unmarked pipes from floor boards both capped off, which one is the hot?

Always put the hot on the left. Can always change the caps if it's the other way around

Put a service valves on each pipe, which will allow you to isolate it locally once you have finished putting the taps on, you will be able to test which is hot and cold, if they are the wrong way round it is easy enough to swap the two pipes around that feed the taps.

turn off all your water fit service valves on pipes,then turn on water and test to see the hot one, connect correctly cold on the right hot on the left, it is done this way for partially sighted and blind people.

Isolate the water and put 2 service valve and connect your flexi hose on to it , normally the one on the left should be Hot but even if it’s not you can just swap your flexi hoses. Test it , job done