How much power supply (how large) you need depends entirely on how much current will be needed by all the things connected to it. One way of determining that is by just adding up the fuse sizes, add a few amps for an 'over-head'. The larger that 'over-head' the better off you will be, you could add a few more gadgets with no problem (there'll always be just one more thingy that you wish you could add, you know?).
There are two ratings for power supplies. One tells you the constant current supply (CCS) the thing will put out all day long. The other tells you how much 'surge', or intermittent current supply (ICS) it will handle. That ICS is always more than the CCS, and is the most common rating shown for power supplies, the one you usually see quoted in catalogs. That ICS rating is only what the thing will supply for VERY short periods of time, as in a second or two. That CCS rating is the biggy, what it will do for almost ever with no problem. The difference between the two is something on the order of 30 to 50% (there's no particular 'standard' for that difference). So it amounts to "bigger is better" until it get's absolutely ridiculous.
Good luck.
- 'Doc
