it should say on the reg what it is compatible with. The main reason regs and tanks are different is the various compressions/properties of the gases. Regulators are very tough things and designed to hold up for a long time. The metals and seals in each type of reg are specific to give the greatest resistance to the gas it is designed to use. As far as needle valves i would think those are a bit more forgiving, but main issue I would see is how fine of accuracy they have as you do need pretty fine accuracy. Also threads/ports/barbs on the needle valve depending how you want to hook it up and what size tubing. Needle valve for aquariums are typically not that expensive unless you are aiming for something thats top quality.
For a CO2 tank, I would highly recommend just browsing Craigslist for a used tank. Thing is very very few places 'refill' a tank. What they call a refill is really just a swap and whatever tank you give them you won't likely see ever again. Your ownership just transfers from tank to tank. All you pay is for the CO2, which for me is roughly $20 for a 5lb tank. So IMO don't bother trying to hunt down a nice CO2 tank to start with. They come in steel and aluminum, both work fine.