Sounds like you're further ahead than I am with those enhancers! Honestly, I don't want to try and give too much advice, because I am still figuring things out as well. Personally, I think the water tower is a great deal, but the 30min cycle requires a lot of attention if you really want to maximize it.

Idk, it is very easy to work yourself broke where you find yourself penniless while waiting for items to sell. So just because something sells at a higher price doesn't mean it is the best strategy for your situation. It may be more beneficial to have higher volume/lower gross than vice versa.