Yes, that would be enough. The amount needed depends on what exactly they're testing and how much they need to test to gather enough data to make a decision.
Solubility testing will use very little to see how good the solvent is at cleaning up whatever sludges/waxes you are concerned with. If the goal is to improve flow properties, it takes very little to develop a viscosity blending curve as well.
It's unlikely a company with serious considerations would order less than a gallon. So for $33, assume as a best-case scenario that 3 companies ordered a gallon for testing.
Yes. Unless "more machines" means "more machines than the zero we have". Maybe they can't make the product themselves yet and have to contract it out or manually prepare each gallon.
For the purposes I would consider it for (sludge removal, viscosity reduction), yes it's not cost efficient.
If the application is "paraffin removal to improve pipeline reliability or extend production of a well", then I'm not really qualified to guess. Totally outside of my area.