That
CO2 is a great system, but not for a tank this size. I used 2 of those for my 55 and finally ditched the ladder diffusers and ran the air line tubing into my canister filter, and it was still not enough
CO2, though it improved dramatically. I am now using 2 large juice bottles for
DIY CO2 (sturdier than soda bottles) and a powerhead diffuser, and am able to maintain 25-30ppm
CO2. I have higher light, so it is important for me, but if I could do it all again, for a tank of this size I would go with pressurized
CO2 and be done with it, with a greater initial cost but savings in the long run.
As far as substrate, if you are into a more natural looking tank, go with the regular Fluorite (the red is really, really red!), and you will be all set for your plants. I have done the retro-fit substrate in a big tank thing, and you should save yourself the trouble. You might need more than 3 bags, but use the "sand bed" calculator here on this site and see how many pounds you want. 3" would be ideal,
IMO.