There are all kinds of substrate out there at all different price ranges, you should first decide how much you are willing to spend on your substrate and work from there. I have Activ-Flora substrate in my 75 gallon planted and a 10 gallon planted and it works very well, I have been using it for over 3 years and have never had a problem. If price doesn't matter, go with Aquasoil.
The size of your co2 depends on how often you want to fill it and what store are in your area to fill your tank. In my area there are only tank exchange programs, no one refills them. So I stuck to a paintball style regulator and tank system, I usually get almost a week out of a single tank, I am currently testing it to see exactly how long it last me.
There are a bunch of websites out there that sell Co2 equipment, just like the substrate you need to decide how much you want to spend on the regulator first, most people here will tell you to go with GLA, they are a wonderful company but have higher prices than some of the other options out there. There are several people on TPT that sell regulators as well. But a good general use regulator for an aquarium can be found in many places. Keep in mind that for an aquarium you do not need a super expensive regulator, you just need one with a reliable needle valve, and if you don't want to turn it on an off manually a solenoid.