55g planted tank.

Pressurized will be far more easy to control CO2 levels.

from all of my reading i'd say you;ll need pressurized. if you were going to do DIY you'd have to have numerous soda bottles and regulation would be a nightmare.

Depends on the light wpg and the type of plants actually. Higher light levels will require more CO2, especially with fast growing stem plants.

DIY should be sufficient, especially if you use Excel along with it. But of course pressurized is best for regulation and ease of use. So expensive though. Is it really worth it?

I'm partial to pressurized because that's all I've ever used. It's easier to be consistent with pressurized.

You could probably use DIY if you want, no reason why you couldn't. It will take more maintenance work to keep it running though. After a while I think pressurized will work out to be the cheaper option. Might take a couple years.