Warming your water change water will help to dissolve the salt both more quickly and thoroughly. A basic 150w heater like an eheim jager is about $25. That and an el cheapo $10-$20 amazon powerhead and water mixing is faster and easier. Bonus now you're got a spare heater on hand for your tank...
If you have the original boxes and paperwork I’d like to have it. I’m sure it won’t fit though. I happened to see in your mushroom sale post that @Wilson416 is coming to you to buy and pick up. I know him from Njreefers. Maybe he could pick it all up for me and I could pick up from him. Let me...
Yes, I’d pay shipping. I see usps has two different what they refer to as medium size flat rate boxes. One is 14”x12”x3 1/2”. Would they both fit in that? That box is $16.10 flat rate.
This 15g is the largest I've found; https://www.saltwateraquarium.com/hydrofill-ti-ato-water-reservoir-15-gallon-innovative-marine/. If you require bigger, you can really use just about anything you want. Plenty of tall tanks that can give you volume with a smaller footprint. I have a 37g tall...
Your location just says North Jersey, so not sure if this helps but there's a seller on FB marketplace with nice chaeto in Randolph. $5 for a pretty good sandwich bag full. I purchased from him a couple months ago and it's good stuff. I can give you his number.
Based on the locations you posted Sea Level on rt46 in Pinebrook would be your best bet. Reefco in Boundbrook would be second. What are you looking to purchase? There are private sellers I could recommend.