Hey Rich,
:welcome:
Dissolved O2 will not be necessary. A TDS meter is helpful to know when to change the DI part of your RODI (assuming you have one). If you plan to stock calcifying corals, then Calcium and Alkalinity will eventually be the parameters you check most frequently. Ammonia and Nitrite are rarely needed after the initial cycle (and could be avoided altogether if you just allow plenty of time to cycle). Some people test for Nitrate often, to know when to do a water change. Phosphate test kits are notoriously difficult to read, and many do not measure in fine enough detail. (They are worthless, IMHO. If you have nuisance algae growing in your tank, then you can be sure your PO4 is too high. That's all the test you need.)
With the exception of TDS, all of the above are usually purchased as titration kits. There are expensive electronic versions of some, like PO4, but they are very pricey.
And always-on electronic Ph monitors are neat to have, and interesting to watch, but not necessary. I would wait until you get a Ca reactor and buy a Ph controller (not just a monitor) at that time.
HTH