My rigid mountain bikes with slicks is currently running 36/16 and I wouldn’t run anything bigger because the hills are hard work. I spin out around 18mph,are you guys really spinning out at 20mph with those big gears?
My commutes are short at 5miles each way. I happily wear the same Base Layer and shorts all week in the winter. In the summer I rotate a few pairs of shorts/Base layers and wash them all on the weekend.
Have never used clipless pedals so may be completely wrong here, but new pedals should come with the appropriate cleats, the cleats are then screwed into the holes in the picture you provided. So the shoes should be compatible with all pedals.
Been teetotal since I was 18,so 14 years to date. The wife is a social drinker but e don’t have any alcohol in the house anyway, but it really is quite easy and If people do find it difficult than it is perhaps a sign of a drink problem.