a few newby questions

To answer your first question, no you do not have to remove the sponge material from the roots that came in the pot. If you choose to remove it though do so carefully in order to preserve the finest roots. But even if you rough it up a bit it's extremely unlikely that you'll harm the plant beyond saving. There is going to be some die off before the plant takes hold anyway. Burry the roots so that the crown is just above the substrate. Wait a week or so before adding any fertalizer. Then after the plant has settled in push a root tab (for aquatic plants only) as far down as you can near the root system. Be patient and it should be fine.

As for the bubble counter, I say ditch it. It's unlikely you're going to need a bubble counter for DIY CO2 unless you're intentionally overdosing. Speaking of which you're going to need more CO2 than what one Hagen DIY kit can dish out. The Hagen canister is 1 liter. I have 2 liter DIY CO2 connected to my 20gal and it's barely enough to keep me at 20ppm. I like to see it a little higher.. around 30 - 35ppm. That's where the plants start pearling under high light. It's very pretty.

If you're looking for a good background plant consider Vals or Hygro. There are many varieties of each. The difference is that Vals are root plants where as Hygros are stem plants. The Vals propgate by runners and are difficult to manage, but I've succeeded in getting mine to propogate only near the back wall. Hygros are considerably easier to manage becuase they only propogate along the existing stem. Some hygros, such as Hygrophilia Polysperma, may grow 4 - 5 inches per week under the right conditions. Others such as Wisteria (Hygrophilia Diformis) grows at a much more reasonable pace but fills in nicely. With your lighting and significant CO2, you're going to see substantial growth with whatever you choose.

My only suggestion would be to change the bulb to a 6500K. The reason being is that chlorophil is tuned to both Red and Blue sides of the spectrum. The 6500K bulb is more full spectrum, versus the 10000K bulb which is more blue. You'll probably do fine with either, but you will see healthier growth with the 6500K because the plants can utlize more of the light.

It is best to carefully remove all the packing that the roots are encased in as it will give the roots a better chance at spreading and by removing the packing you are removing an over abundance of nutrients that come with it. These extra nutrients are necessary for the 'forcing' of the the plants, by the grower and can/will cause algae issues if allowed to get into the water table of your aquarium.
In short, you don't need it so I'd advise that you lose it.
You don't mention the tank in question for suggestions for a background plant and without knowing the height you want to fill it's difficult to recommend a plant for it.
I agree with the above post on the bubble counter. Test for kH/pH relationship for the best read on CO2/ppm.

Len