IMO, unless you're committed to doing a fish-less cycle, you're going to want to go ahead and buy salt pronto: you don't want to have to be taking a trip to the store for more every time you need to do a water change, or for quarantine, which you should
most definitely be doing. Even in a brand new tank! Marine ich for example can sit dormant for up to 76 days in a system, meaning if it shows up in the tank, the only way to get rid of it is to either treat the whole tank (which means using medications unsafe for inverts) or to quarantine and treat your fish and coral livestock while you let the entire system go fallow for those 72 days to preserve your inverts. This is just one of
many possible pathogens that can show up with new livestock, live rock, etc.: there are many more to be equally - if not more - worried about that only QT can help abate.
And honestly there's little to no reason to do a fish-less cycle. Between the bottled bacteria you have, the availability of cycled media from other club members, and the ability to buy pods either online or from an LFS (you want LOTS of pods), they'll help shorten all the ugly phases by a LOT. By starting with a couple of hardy corals and hardy fish (like clowns), you jumpstart the entire cycle right from the beginning.
It's a choice between several weeks of QT to be
sure all is well, and the risk that you may lose livestock or even completely crash the tank leading to a complete reset. It's a process that really shouldn't be skipped, and basically, you either medicate (which you want to use a dedicated QT tank for, because copper medication is a pain to completely scrub a tank of), or you do a tank transfer method which is going to see you mixing up a new batch of water as you switch the livestock between two QT tanks every 2 days.
Either way store-bought water isn't something you want to rely on for that process. You won't need as much water if you medicate, generally speaking, as with a tank transfer method, but you MIGHT just need it when you don't expect it, either.
Not to mention, switching salts can be something of a shock to a tank - particularly a small one - especially if the levels of elements, etc., are wildly different. IMO, it's best to pick one and stick with it, if at all possible. If you do wind up using the store's water, either try and get the same salts they use, or else make sure you do small, regular water changes while switching to a new salt so you accomplish the switch gradually.
Note: Some people successfully switch salts without major issues, but many also struggle with it - the main risk is in large, sudden changes rather than slow, methodical transitions.
As for the Hanna checkers? Probably worth it, at least over time, but for only some tests: Alkalinity (dKH), Ultra Low Range (ULR) Phosphate, and High Range (HR) Nitrate are all broadly useful.
Calcium is worth testing if your tank has a high demand - like if you're keeping lots of LPS/SPS corals - but the Hanna checker gets mixed reviews for accuracy, with comments noting it can be finicky compared to their other testers.
pH is an absolute necessity - you should be testing it pretty regularly, as stability there is
&
.
If you don't have an Apex unit or some other continuous monitor, you'll want a pH tester without question, and probably the Alkalinity tester also. You only need the other ULR Phosphate and HR Nitrate if you're trying to fine-tune nutrient-export / -balance, or dosing nitrates intentionally. You could also get a pH pen, or a Seneye device, for a fraction of what an Apex costs.
