Drivers were usually polite and seemingly careful, mercifully light on the horn. As for Bangkok itself, only the truly mad would attempt to cycle there - I did, and it was one of the silliest things I've ever done. Sadly, there weren't many push bikes in the provinces. The only cyclists seemed to be children, or the very poor, though I did once see a team of monkey-handlers travelling by bike from village to village for the coconut season. On the other hand, I was surprised to meet a dozen or so foreign cyclists, quite by accident.
Every town has a cycle shop, dealing in Chinese-style clunkers mostly.
Ten speeds were not uncommon though, and some shops sold basic MTB's. A degree of mechanical self sufficiency is essential. A large, cyclist size meal could be as cheap as a dollar from a market take-away stall, or around two dollars in a restaurant. Thai food is very spicy, and served cold, but you get used to it. There were markets for fresh vegetables, and I could always find tomatoes, onions and cucumbers.