Normally the regulator fits directly onto the tank. Regulators used for welding are favourites ('cos they're cheap) but folk like CO2 Art do very nice ones for fish tanks (careful, some fish tank ones are just "flow regulators" and do nothing for the pressure).
What regulator are you trying to fit? The tank side needs to take the 8-900PSI from the tank, and it should regulate down to 0-4Bar (0-60PSI). These "primary" regulators are fairly coarse in their adjustments, and to get finer regulation you have "secondary" regulators that can't take the tank pressures, but provide finer control (I have secondary regulators to get 7.5-10PSI adjustment from the 4 bar "primary").
Lots of places sell "beer line" pipe to get the CO2 where you want it. And there is a wealth of "john guest" fittings to connect the pipe to where it's going to (or coming from) including connecting to corny disconnects. 3/8" pipe does the job for CO2, but you might use 5/16 or 3/16 pipe for moving the beer about.
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