Because of the supports, I'd either keep the tank vertical as designed, or add some supports along the glass-only corners if you decide to turn it on it's side.
(You could just use right angle wood molding from local hardware store & paint it black to match...make sure it's the same identical thickness though.)
Humidity: tends to disappear no matter what your local area has, since cages & our homes are heated or A/C'd...the humidity gets pulled out, but easy to raise it
with the right substrate that holds it. I'd skip newspaper or aspen, they don't help.
Ambient temperatures: keeping your house that cool will be a challenge to keep this tank warm enough with UTH alone. You never want to heat the whole
floor of the cage, of course, but you might heat a bigger proportion of the floor with good thermostat control. (like half the floor) Also, I'd plan on INSULATING
this tank...styrofoam & many other materials can work well. In fact wood is great too, cork tiles, whatever...I'd cover the sides, back, & bottom (leaving room for
the UTH to safely "breathe"). Many prefer plastic tanks but I'm not one of them, & plastic loses heat too...mainly ppl like the humidity retention, but that's only
because they have minimal air-flow, something you can do with a glass tank as well.
The main thing is to test this out thoroughly with heat running BEFORE you try to house your new pet...to leave time to shop for or order additional products
if needed to achieve the right temps. year-round.