MOST Deuce owners are best served with a 0-15 PSI boost gauge. Unless you really crank up the fuel, a C turbo will typically max out at around 10 PSI, a D turbo will do a couple of PSI more. With that said, there are members on this board who have reported boost exceeding 15 PSI. I'd suggest starting with a 0-15 PSI gauge, if your turbo pegs the needle you can always sell it on Ebay and replace it with a 0-30 PSI gauge. For most of us, the 0-15 PSI gauge is the better choice.
I went the opposite direction, and started out with a 0-30 PSI gauge. My C turbo only put out 6 PSI max originally so I bought a 0-15 PSI boost guage and sold the 0-30 PSI gauge on Ebay for near what I paid for it. I also installed a pyrometer and used that to conservatively adjust my fuel delivery, but my max boost is still only 8 PSI.
If you do decide to adjust you fuel delivery rate, install a good pre turbo pyrometer and adjust the fuel to keep your exhaust gas temperature below 1250F at worst operating conditions. If you can only afford one gauge, get a pyrometer. A boost gauge provides interesting information but there is little that you can do with that information. A pyrometer provides valuable information that you can use to improve your Deuce's performance and/or prevent engine damage via the fuel delivery adjustment route.