A few things.
Firstly, RSO is a bit of a misnomer, since RSO is technically the term for what Rick Simpson advocates, which uses isopropyl (rubbing) alcohol and doesn’t freeze anything. While iso is poison, you also evaporate it until there’s theoretically nothing left, but as you’ve gathered - most folks are more comfortable with ethanol since that’s safe for humans to consume so residual solvent isn’t an issue. A more accurate name for what you’re doing with ethanol would be “FECO” (full extract cannabis oil) or “QWET” (quick wash ethanol extraction) - although QWET is technically a technique. There are other names but generally those are the two biggies.
Freezing the ethanol is only half the equation though - you also generally want to freeze your cannabis as well. The reason for this is that THC remains quite soluble at very low temps but certain undesirable compounds are a lot less soluble. Namely chlorophyll, waxes, water, and lipids.
So what folks do, is freeze their flower and ethanol as low as they can get it. Lower the better. Using a chest freezer is best as they’ll go down to -25C or lower. Some folks even use dry ice or a medical freezer to hit those -40 temps. Then they do their soak (called a wash) for a few short minutes, usually. 3 minutes is often the recommended time although the lower you go, the longer you can soak. It also depends how certain you want to be that you got everything - lots of folks will do 5-10+ minutes soaks at these temps but you are risking dissolving all the stuff you’re trying to keep out, so I’d keep it to 5 minutes or under.
Typically you do two washes to get 95%+ of the THC. So you do one soak, then filter it, then do another soak with fresh ethanol, then filter again.
The filtering is a key part of getting very clean cannabis oil. Folks will use Buchner funnels and fancy filters to really dial it in but you can also get great results with just a few coffee filters stacked together. After you filter both washes, you can combine them and do a winterizing step. This means freezing your collected washes for 24+ hours to ideally precipitate any of the waxes and lipids and such that made it through the filtering process. You then filter again to try and get this stuff out.
Now you evaporate the ethanol away. Either open air, with heat (don’t explode yourself), or in a special device like a Source Turbo which will reclaim the ethanol for future uses.
What you’re left with is a fairly pure (maybe highly concentrated is the better term) oil. Make edibles with it, make vape carts, make shatter, make pills, make sublingual drops, etc - do whatever you like with this oil.
Regarding water - yeah, it’s not your friend. Lots of folks have issues keeping water out of their ethanol - that’s condensation for you. It can cause splotches in your oil and such because water doesn’t evaporate away as nicely as ethanol. If you get water in your ethanol, it’s not the end of the world, but it will take longer to evaporate it out than the ethanol.