Your butt will get sore until you're used to riding, and each spring when you start again. Some better shorts wil come in handy, synthetic chamois vs the cloth liner you have now. Cloth is OK for short rides, but not much else. Wear your shorts next to your skin, and use clean ones each day, of course. Chamios fat/cream or noxema will help as well, talc on the cloth.
Spinning-
I've been riding seriously for 30 years and have to work on my spin every spring, working on my ultimate spin speed 160 + for a few seconds, (until my tongue hits the spokes). The faster your "ultimate" spin is the better your stroke will be. I try to ride during the season at 100 rpm but rareley do. I try not to use the big chainring until I HAVE to, well over 20 mph, and never during the beginning of the season.
Circles- Don't just push down on the pedals push forward, down and then pull back like you're trying to scrape something off your shoe. Make your force go at right angles to the crank arms, but take it easy on pulling up.
ride smart
Pat