you will need a whole lot more bottles for a 6ft tank. i have a 4ft, 50gal tank and have 4 2l bottles hooked up, 2 on each end.
"enough lights" depends entirely on what sort of plants you want to grow. how many watts are your lights, and how many gallons is your tank? if it is about 1 watt : 1 gallon, then you are good to go for low light plants.
50gal planted - yoyo loaches, BNs, odessa barbs, giant danios
33gal planted - praecox rainbows, gold ram, bolivian rams, sparkling gouramis, licorice gouramis, lots of shrimp
2 x 5gal planted - bettas