It’s not a full latex face mask, it’s a half mask with a cloth balaclava back, so it does breath and doesn’t trap the heat like some kinds of full head orc masks.
On the field the monster crew have plenty of water carriers to make sure you keep hydrated, also you die often enough as barbarians that you can take a breather and get fluids regularly. You’ll usually get reminded to drink as well whenever there’s an opportunity.
So yeah you don’t really need to take more care looking after yourself on a battle than you would do without a mask, in my experience.
With some of them. You may have to go through a few to find one that will fit from the general supply. usually best to put the mask on and then your glasses, feeding the arms through the side of the eye holes.
If you want to guarantee having one that definitely works buying your own and adding appropriate holes is probably a good investment.
You may also want to look at one of those sports bands that help hold your glasses on your face too, saves having to worry about them when dying repeatedly.