If you're going to run DIY CO2, I'd definitely run more than one. I want to say around 3, but I'm not too sure on that and maybe a more experience member can help.
As for lights, i have an 80 gallon and I have about the same amount of wattage you do and the plants are doing great. I would say you have enough lights.
What are you plans for the tank? Is it going to be fully planted or sparsely planted? Any hardscape(driftwood or rocks)? What help me was going on MS paint and designing the layout i wanted with the type of foreground/background plants and fishes i was trying to get. This gave me a plan and it made it much easier.
As for dosing, I personally use the EI method because it's much cheaper in the long run. Check this thread out, should give you want you want to know...
http://www.plantedtank.net/forums/fe...-regimes_.html