I would add some onion/shallot first, which would add sweetness, then sugar at the very end if it still needs it. Rather than using cooked potato for thickening, you might consider using a potato starch slurry - that would thicken better with less of it than cooked potato. In general, pepper seeds can be very bitter so I think it's important to be vigilant when eliminating them before pureeing.
Edit - plus one for the tomato.... if you want to double down on the roasted flavor, you can char the onion/shallot, then rinse as much of the char off as you can... or just use some canned "fire roasted tomato"
