HI.
I recommend that you initialy build your own lab to prepare yourself, not only read documentations.
For the planning phase - I recommend that you ask someone to assist you because you might find out that additional software/hardware or both will be needed for specific tasks - for example proxy/contecnt filter/syslog server/log analyser/AAA or other like the VPN concentrator that you already plan to use.
Placement of the VPN server is an important issue that should be planned.
Planning for ip addressing, routing, NAT and DNS are also very important.
What pix version are you going to buy - the R or UR ?
You might find it useful (but more expensive) to purchase 4 interfaces or more, and use a dedicated interface for specific tasks like VPN server or other.
So my advice - get some more help in the planning phase (not only pre-sale), it will probably be cost effective versus doing it by yourself.
Learn about the pix capabilities and limitations, and plan for additional supporting software and hardware.
Bye
Yizhar Hurwitz