PSU and fan connectors question

I have a Raidmax case , power supply and case fans with a Asus P5AD2-E premium MOBO,looking for opinions on converting the 4 pin fan connectors to 3 pin to take advantage of Asus Qfan 2 , and fan monitoring on the motherboard. I am concerned with the power draw on the motherboard from the 4 case fans, and with a prescott( p4 650) processor, if the fans would ran near max anyway with the prescott heat issues.
Also the raidmax 420 watt PSU is a 20 pin power connector for the motherboard while the Asus motherboard uses a 24 pin connector. the Asus book says it can be used if its rated at least 15A on the 12v lead(which it does) and provides at least 350w. Anyone know of the drawbacks of using this PSU or should I just buy an EATX PSU.

first build, still have doubts, and insecurities !

 

As for converting 4 pin fan's to 3 pin to connect to your MOBO fan headers, Be aware that there are limited amount of voltage avaible on those fan headers, if you exceed that amount you can burn out your header.
You can just connect the monitoring wire to your mobo, and provide power directly from the PSU/molex connector.

That raid max 420w is Low end of the Quality scale, the PSU is not an area to skimp on Quality, If was mine, I'd replace it with good Quality one, 24pin.