I could be crazy, but I’m pretty sure you would be fine just using dechlorinator. I would buy locally and you’re most likely fine. Just my opinion. I’ve lived in a soft water state and now hard, I’ve never had an issue that a fish couldn’t acclimate to my water. I don’t keep sensitive fish like discus, do my regular maintenance and I’ve never had an issue. Over time, you’ll be able to notice things with a quick glance of your aquarium. I think you might be overthinking this a bit. If you want to tinker by all means, but as my doctor told me, sometimes it’s best to stay off webmd.
ps that’s not discredit the fine advice you got above. If you decide to continue then you got some good stuff up above.