I started about 8 months ago, had a lot of the same questions, the test kits are less impactful early imo then you think. I use my Alk, Phos, and Nitrate the most. Weekly for Phos and Nitrate and Alk more often as my tank grows and I am tuning in my Alk dosing.
RODI, I had one from the start, if I didn't I would have bought one instantly, there is zero chance I want to drive to the LFS to pick up RODI as often as I would need it for my tank.
ATO - less worry on salinity swings and also just one less thing you have to do daily. Fill up your reservoir as often as you need it and then forget about it other than testing your salinity.
Dedicated heater for salt mixing and a python to move your water in and out. These things just make the weekly work much easier and make me way more likely to ensure I do it.
Scraper, my tank gets very nasty early as its still building up its diversity, without a decent one it would have been much more of a pain in the butt.