Congrats! This will be a fun ride for you.
I don't have anything to contribute regarding US suppliers, but I will say this - don't worry about 30" rolls of anything. I'd recommend sticking with 54" rolls as they're more common.
If you want to stock different sizes of anything, I'd do 38" / 54" / 63" wide rolls of Duratex 13oz DSS (Grimco) as these sizes will work efficiently for 3' / 4' / 5' wide banners. The stuff is pretty cheap too, sell a banner per roll and it should pay for itself.
Otherwise here are our main materials that we use daily, all stocked in 54" wide rolls:
General Formulations 201 HTAP (Pretty much all our decals,
signs etc get printed on this)
3M 40C-20 (Wall wraps, some decals)
3M IJ180cv3 (Fleet graphics, wraps etc)
Oracal 3651 clear (Clear decals, acrylic prints etc)
Avery DOL 2080 matte (Solid calendared matte laminate)
Arlon 3220 matte (Great cast dead matte laminate)
3M 8418G (Every day cast gloss laminate)
Drytac 5mil Emerytex (Textured laminate for durable applications etc.)
We don't mess with
paper or canvas, so can't comment on those.
Hope that helps. I wish you best of luck on your journey. It's probably been close to 15 years since we got our first printer (Roland as well) and it was a big stepping stone for us.