Welcome Pub! Let me take a crack at your questions.
1. Yes, they may be watching you, they may be thinking (or saying), "Look at that big/fat guy trying to ride his bike". Those people suck, but let them push you, you are riding to better yourself and if they don't hate on that, they'll find something else. The best part of people like that is they are not doing anything for themselves. Other riders will applaud your efforts, and before you know it, you'll be encouraging others to take control of their lives and ride too. What I'm trying to say is, "be the inspiration you are looking for".
2. So, you're not fast, you don't need to be. Speed comes with practice, the more you ride, the more efficient you will become, and thus you will gain confidence. This brings me to...
3. Shifting is difficult at first, but becomes second nature over time. I suggest looking up some videos on the matter.
http://bicycletutor.com/gear-shifting/ Practice makes perfect.
4. I didn't notice what kind of bike you are riding, but there are many that will hold big guys like us. Mine is a variation of the Trek Navigator and has held solid for thousands of mies with very minimal maintenance.
TheStoutdog on his steed:
Most importantly, get out and ride. You'll be surprised how quickly these concerns will fade away. Good luck and have fun!
