I can't help on the location of the resources folder, as I don't use the facility.
Glad you kinda got things sorted, I'll just repeat before leaving, don't use the resource folder for Rapidcart. It might work OK(ish) initially, but once you have a lot of a product in your online shop it'll slow down editing massively.
The concept of the resource folder is good, but it's old and best avoided now, for many reasons. Search this forum to read why. If you're just starting out get in the habit now of warehousing all your images, not just those for Rapidcart.
You absolutely will regret becoming on reliant on the resource folder soon, sooner or later you'll switch to warehousing, the sooner you do it the less painful it'll be.