First, this is just a good read:
https://www.reef2reef.com/threads/the-supreme-guide-to-setting-up-a-saltwater-reef-aquarium.138750/
Basically to answer your question, yes. So I make RODI water in to a 32 gallon brute trashcan. has a float valve at the top that stops making water when it is full.
In my specific case I generally only use this for topping off my ATO container.... IE, I'm the oddball that does not do water changes.
For you, you'd take 5 or 10 gallons of the rodi water in to another container, throw a powerhead in there, heater, and mix your salt for a water change. Pump 5 gallons out of your tank, and put in the new salt water. Done!
As for testing, most people's big three are Alk, Calc, and Mag. Calc and Mag are fairly hard to test for in home aquaria. I'd call the big 3 ALk, Nitrates, and Phosphates.
If you maintain a stable ALK, and you almost certainly will with regular water changes, you have a very good chance of maintaining good calcium and magnesium levels.
Nitrates and Phosphates have a WIDE range of accepted values. What you do not want to do is have zero of either or both. You will ignite a major algae problem.