it does help get rid of the yellow colored tanins
Purigen in your filter will also pull the tannins out of the water really quickly if you put some DW in without soaking/boiling it first. I had a tank that was practically coffee colored from the DW leeching so many tannins in the water, and it was crystal clear withing 24 hours of adding purigen to the filter... almost like magic
I also had a piece of DW in my 55g that would not sink for anything - I ended up floating it in the tank for nearly a month and then weighing it down.. it eventually got waterlogged enough that it stays down without help, but it took a surprisingly long time.
As far as where to go with your tank.. what do you want it to look like? Personally I'd add some driftwood or at the very least some rocks and some taller stem plants in the back to hide the heater.