I agree with Alan that you will get truely lovely prints on the appropriate coated card stock, use the manufacturer's profile, that said I have printed on plain heavyweight paper quite successfully which is fine for mass printing of cards on my 3880. I even sell cards printed this way. The lower cost allows me to sell at a price point that works for me and the retailer.
Just don't sell them as "fine art"; they are not.
I set the paper to premium enhanced matte and use MK ink. I have the ink density reduced to -20 paper thickness set to 3 and platen gap on auto
I suggest playing with the ink density to find what works best for your paper. Save as a preset.
There is a learning curve to using this printer, be methodical, re-read the instructions, repeat.