Ref. cool churches. I used, as a young organist, to carry out my practice in a variety of unheated churches - one, in particular, I was able on many occasions to stay there for up to seven hours.
I've found, over the years, that one simply gets used to it. (This has later financial benefits, in, for example, not needing heating in the house to be 'on' very often.)
Also, finding one's way around SATB hymns is, as many have said, not a skill which necessarily comes easily. As a result, it's as well to approach it systematically, i.e. initially for manuals only, S, SB, SAB, TB, AT, SAT, STB, ATB, SATB, and so on. For pedals, separate the bass out, and do not duplicate it in the LH.
Training in this manner, though at first seemingly laborious, will repay itself by preventing too much unlearning of suboptimal habits later.
Finally, a rant: please don't be beguiled into the foot-pedal tautology!!!
Best of luck,