Is there a way to sell a product in-store through Squarespace, but not offer it online?

We recently moved our website over to Squarespace from a third party programmer, and also ditched Ecwid because they increased their price to synchronize their inventory with Square from $35/month to $99/month. We have a Square iPad stand with the cash register, and just set up the Squarespace app to start selling our online inventory in-store using Square's hardware. So far so good, with no complaints. I do, however, have just a few questions, as this is a new inventory system for me and will take a while to figure out all of the details.

1. We have products available in-store that we do not sell online. We are a sawmill that sells kiln-dried hardwood, but we cut our boards to 2' sections and sell those boxes online. In-store, however, our boards are 8' long and we sell them by the board foot (A square foot by an inch). Is there a way to include all of our in-store products on the Squarespace app, without actually displaying the items online? Apologies if this is a stupid question with an easy answer. Like I said, I'm new to this system lol.

2. Is there a way to change the units that we sell the item in? In Square, I could set my own custom unit. I called it "Board Foot", because that's what we sell our lumber by, and was able to set multiple prices per board foot. Is there a way to also make custom units in Squarespace?

3. On the Squarespace app, is there a way to display by item category, rather than just a giant list of all of our products? That will make it much less of a headache when we go to ring somebody up in-store. Again, this may be a stupid question with an easy answer, but I have a lot to figure out right now so if somebody could effortlessly answer it that would just be one less thing adding to my headache.

Thank you!