just ride and don't think too much.

you'll adjust when needs to be adjusted over time as it's an evolutionary process.

i ride a super hard MTB seat 15 mi/day round-trip and it's not a big deal.

i started commuting in the summer with some beater Old Navy cargo shorts ($5) and fake wool long-sleeved ($8) shirt I had kicking around. that worked fine when it was warm. in the winter, i bought some inexpensive lycra running pants (€15) a technical XC ski top (249 SEK) and a hooded XC ski stop with zip to cover the neck and prevent air going down my front (699 SEK) and an L.L. Bean weatherproof outer shell ($69). some XC ski gloves keep my hands warm down to -5C/25F. any colder than that and I need to flex my fingers when riding.

as far as shoes go, i have some Nordic Walking shoes from Adidas with Gore-Tex that I bought for a trip to SE Asia (€50 at 50% off) that work wonders in bad weather and cold down to -5C/25F.

good luck and let your bike/attire evolve over time to meet your particular riding conditions.