Hello RP8.
Welcome to our Mattress Forum 
and welcome to Texas!
Well, you’re in the right place.
Beloit is a Trusted Member of our site, so we fully trust their product quality and their sales practices; in the Texas area you may also wish to visit The Mattress Factory and Texas Mattress Makers (@Texas_Mattress_Maker)
Not necessarily. I tend to sleep hot as well, but can sleep fine on foam that is covered by a natural layer (like cotton or down). Memory foam directly under the body collapses under your body heat as the night progresses, which is why you sink so much into it but also why it can feel like it’s progressively warming up. Your body heat stays trapped between you and the memory foam. That said, this occurs most with thick layers - a thin layer isn’t likely to be a big culprit here. There’s also so much more that goes into the mattress microclimate that you may find interesting
It definitely makes a difference for temperature regulation! Wool and cotton at nature’s natural temperature regulating tech The thing with natural fibers is that it can compact over time, creating a firmer sleeping experience. So if the layers are thick I’d keep that in mind.
So, it’s hard to say for sure what your perfect sweet spot is. You and I have almost the exact same sleeping stats and I’d punch the sun before I’d sleep comfortably on a firm mattress. I think in your case, buying from a company that offers a sleep trial is going to be your best bet. I’d personally lean towards something with a little softness to sink into (i.e the luxury firm feel).
Totally up to the buyer. Mattresses these days, at your stats, made with durable components, are going to be lasting 10-20 years anyway…some people really love flippable mattresses (especially the ones that offer two-sided firmness options like the Nest Bedding Raven.
Once you’ve narrowed down a list of mattresses, I’d be happy to look at them and make some commentary on which ones may be the best to pursue!
NikkiTMU