Originally Posted by cny-bikeman

You're not an idiot, but perhaps unwise in jumping into buying tools. Unfortunately you've already wasted some cash buying a chain wear indicator when a ruler is more accurate and cheaper, but:

1. Any 5-6 speed freewheel of the ratios you need is probably fine, though you need to make sure you have enough room for a 6 speed between the hub and frame. Generally Shimano is the most available and best regarded, Sunrace is probably next, Falcon lowest in overall quality..
2. Mostly looks and weight, neither of which is critical if you are on a budget, so don't worry about it - get a name brand at the price you want to pay.
3. Not unless the chainwheel(s) are really pointy or have a shark's fin profile. Just ride and see how it goes.

Need to get a chain labeled 6-8 speeds.