Hello,
I've done the CPU switch myself and it is really easy. Philipma1957 has produced a great guide he lists what's required.
For the RAM, 16GB is a good starting number, but you should adjust according to your needs. You could start with that and see how much swap memory is used, and the page-in/page-out ratio (use Activity monitor to find out) after a few hours of intense work.
For the SSD, you have quite a few options. Sticking a modern SSD in one of the HD slots will severely handicap it. It will be bottlenecked to about 275MB/s. It's not bad, but current SATA3 SSDs usually go up to 500MB/s. You can buy a SATA3 PCIe card and plug your SSD either directly on the card, or using a SATA3 cable.
-Cheapest card around: ASM1061 SATA3 card, will let you boot from it, with eSATA ports as a bonus, but weak speeds: 350MB/s.
-Simple system with good speed: the velocity series of card from Apricorn allowing you to put 1 or 2 SSDs directly on the card, thus leaving the 4 HD bays free.
-Interesting system using up to four mSATA SSDs directly on the PCIe card come from Addonics.
-There are a lot of RAID systems from highpoint that give max speed and possibilities, but they're more expensive and require you to mount the SSDs in the Mac somehow.
-But currently, if you want max speed, you should look
here. In this long thread you'll find lots of info on the newest PCIe SSDs that can reach 1500MB/s in your 4,1.
There are other options, but those cover the usual ones. Read up before selecting, there are a few details and caveats.
Loa