If I want to create a non inventory item and TODAY we only purchase it... but there is a chance in the future that we sell it also, is it "safest" to make it a Non Inventory Item for Resale and just not actually Sell it right now?

Unless future you wants to create another identical Non-Inv item and lose your history then I would!

Note that Non Inventory for purchase item has only expense accounts and the for resale have expense accounts and income accounts. That drives the GL impact, if you are not reselling the item then there shouldn't be any GL impact to income account (in theory). In that case it seems like a safe idea.

The item will show on Sales transactions if created as resale. Unless it doesn’t create any issue with users that should be fine. Also FYI you can customise the item sublist on sales transaction forms to exclude them if needed.

use the sublist field tab in the transaction form to filter what @Tahir Mustafa mentioned (using a saved search), This way these products wont be available on the transaction form thus no mistakes.

Lots of good insight here- much appreciate it @Bryan Miller @Sam-I-Am @Tahir Mustafa