No problem. I remember what it is like to just get started....Many folks helped me..
YES! This is important...Light is what drives the rates of growth, regardless of TYPE of light. A deficiency in c02 and/or nutrients can occur at ANY lighting level, but is more common at higher light...You need to ensure that the plants get NON-LIMITING amounts of c02, macros, and micros/trace elements to grow well, w/o adversely impacting the health of fish and inverts.balance it out with how much lighting there is
Remember that diffusers can get dirty/clogged and then do not perform as well, so this needs to be part of your regular maintenance...
If you are happy with your fluval model, simply get another of the same size. If you go a bit larger model, you can split the outlet in two: one side for surface ripple, and the other for more in tank flow...Remember that it is hard to overfilter...
If you get a small powerhead, you can place this lower in the tank and place the diffuser in front of this flow
Or....you can read the DIY needle wheel (NW) thread and simply use a powerhead with a NW impeller, inject the c02 to this pump, and the impeller will chop the c02 for you. This will then REPLACE the diffuser and has the added benefit of the added flow from the pump itself. Plus, this flow can then be more easily directed around the tank.