You are correct in there being a lot of options and sorting through the options is really a very important point. CO2 can be expensive to get started but it is even more expensive to start in one way and find it not worth the effort!
So a look from my view as each does have benefits and downsides.
I would say avoid the mixing of items to make CO2 as those are not really long term things that will be fun to do every few days or so and they are also not well suited for 55 gallon. CO2 output varies and is not terribly stable.
Step up might be the small cartridge items. Also not good for largish tanks as the cost and time involved in buying/changing cartridges is not going to be good.
Full blown pressure CO2 is expensive but best once it is all in place. How expensive varies a lot. Off the shelf commercial sets that have the regulator to cut the pressure down, a solenoid to act as a "gate" to cut flow on/off and a needle valve to better control that flow can work and they can be had for around $100-150 plus the cost of a tank. But they also have many complaints/defects built in as they are not famous for using good solenoids and needle valves. The reg seems to work okay but the small parts drive many to buy a better set later. Rebuying costs more than buying right the first time, so budget is almost always a factor.
My personal choice is to study the various parts to learn what each does and then shop carefully for those parts and screw them together to fit what I feel works best for me. That is not something some are setup to do, due to time, tools, or personal choices like that. But it can give the best set, built with high quality parts. Downside is obvious, that it does take longer and also does take more effort to screw things together. That last part can be areal bear if one doesn't own a wrench, though? But for the better quality and performance, a guy can buy the few tools needed if it fits what he likes. Better setup/ cheaper price but lots of decisions.