I thought about getting a 20" bass drum for my Renowns, but now I'm probably going in another direction. I sort of retired my vintage 1965 set of drums and that has a 20" x 14" bass drum, now I miss it.
That's a great looking kit. I think a 20" bass would look great sitting under those toms. Autumn and Cherry burst are probably my two favorite Renown finishes.
Have fun with it.
Dennis