What water do you use for your tank?
For your top-up?
With my RO/DI, I don't add anything for top-up ... and just salt for water changes. Depending on your circumstances, Prime might be needed.
Unsure about `Tech Coat', can't really advise on that - but you might not need it.
For calcium and alkalinity - I'd be sure to buy a pair of test kits along with. I've used a variety of the 2-part Ca/Alk suppliments [Kent, C-balance, ESV/B-ionic, Ocean's Blend] and haven't found much significant difference except in price. Personally I lean towards B-ionic ... and if you can check the labels normally they'll tell you `how much' of Ca/Alk contained in each bottle.
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This hobby never quits with the learning.
It's ok, don't get upset about it - and if you get too upset, I'd always suggest buying a good book. There's a handful of quite good ones [rarely I see them in LFS, though] and at worst resale isn't too bad
But we have all been in your shoes, we all started this hobby too.
Just keep asking
before buying stuff and you'll save a lot, learn a lot, and skip a lot of heartbreak/hassle.