Bubble counter isn't necessary, but people will ask on this forum what your bubble rate is if you have any questions, so it's good have one. But also keep in mind that bubble counters are only a rough idea as to how much CO2 is going into the tank.
Drop checker is better for gauging CO2 than having a bubble counter. A drop checker will let you know what the saturation of CO2 is in the tank. You want to aim for light green to yellow color of the 4dkh solution.
Glass diffuser is probably needed out of most of these. The glass diffuser will break down the CO2 into small bubbles so it gets dissolved into the water better. Without the diffuser, with only airline tubing going into the tank, you will get a big bubble out of the tubing which will float to the top of water level and pop, letting all the CO2 out into the air versus staying in the tank