Name change - email Tom Stormcrowe, he can help you out.

Spinning - try using a lower gear. Also, work on it consciously for a few minutes at a time each ride. Spin for a minute as fast as you can without your hips bouncing and hold it for a minute. Rest a bit and repeat. Do 10 such sets. Over time, you find that your max spin improves as well as your regular riding cadence. If you get a cyclocomp with a cadence sensor, that helps you monitor your cadence as well. Comes with time. I too started with a normal cadence of 75-80 a couple of years ago. Nowadays, even at 85 cadence, I feel as though I am slamdancing on the pedals.

As far as components go - dont bother upgrading this bike. Ride it for a while, and then later, get yourself a nicer bike and use this as your commuter/beater.

Riding - make sure you have a banana or two every hour (Snickers works quite well as well). You can also gets sports drinks but unless you are racing or whatever, banana+water works well (I do 60-70 miles on that quite easily). Bulking up - you are in the wrong sport for that. At 130lb, you are one of the few people who are NOT too fat for this sport. Keep it that way!

Sunglasses - any wraparounds will work (I have a couple of Oakleys and a couple of $30 Tifosis - on the road, doesnt really matter. The Oakleys are better at handling sweat falling on them, though, but nothing that I cannot live without). Make sure you have decent peripheral vision on them for when you turn your head to look back.