What's your budget? I would avoid a paintball tank for that size aquarium.
For lower end, I would avoid stuff from Amazon, maybe the dual stage from CO2Art, which runs around $130 from Brooklyn Aquatics, Then find a used CO2 tank on craigslist, say 10Lb or so, depending what size you can fit... try to get a spare too if you like. Don't worry about new unless you know a place you want to use that will fill tanks while you wait. Then look for a time (digital, WiFi or analogue) to hook the solenoid to.
If your name truly means you are in York PA, look into joining the Cichlid Club of York and/or the Aquarium Club of Lancaster County (Both on facebook) or if really into plants, I think it's 1.5-2 hours drive to go to GWAPA meetings each month (I pass through york when I go, and I'm 2 hours before I get to York too)
if you have questions, then yell, if you really want to keep the price down, there is/was a regulator on clearance at LiveAquaria from when Drs foster and Smith closed down, for maybe 30 or 40 dollars.. there were 2 options, and at least one had a solenoid.
hope that helps.