When should I get CO2?

I suggest co2........

thus far your setup is relatively low tech,
so you can get away without Co2 & Ferts.

http://www.plantedtank.net/forums/low-tech-forum/

what would constitute the the cross over from low to high tech?

pressurized co2, over 3wpg, auto water fill and fert dosing systems???

having 2.16 WPG, what do you guys predict I can grow in this tank ? the fact that its 2.16WPG power compact VS t8 make any difference ?

I think you are in the range of CO2. The larger your tank is the less of WPG you need to start using CO2. 2wpg at 60g is mosre liklely to benefit from CO2 then not. Lower it to 96w if you want to avoid using co2.

it's a tall tank. those lights won't do much
more than grow GSA on the top side glass.
do yourself a favor, and keep it all low tech.

Can I make a light upgrade ? I have 2 4x32watt electronic ballasts sitting asside, Can I maybe 4x OD a 48" t8 ? I dont want to limit myself to which plants I can grow cause I have a tall tank. I would even return this light strip to the store and exchange for the 4x65 watt if that will help.

You don't need co2 but any plant will benefit from it.