For what its worth, I would NOT recomend the Hard back books. The only thing i use the Players Guide for is the index. I have purchased everything for the line including 2 core box sets. We play with 6 pc's, and could have just used the free Basic Action Card Download from the WFRP 3 support page, instead of my investing in the second Core box. I work a lot and am going back to school so I don't have the time or the desire to write adventures anymore, so I only use published adventures.
I have read everything available with a few exceptions due to time constraints.
My group uses the following.
GM toolkit (just for the screen)
Creature Vault. ( I prep with creature and action cards so this has been very valuable)
Omens of War (Severe Criticals, Horses, Mounted Combat)
Heros Call (Expanded PC progression, New Races, New Spells/Blessing etc)
The gathering storm Adventure
The Edge of Night Adventure
The Witches Song Adventure
The Enemy Within Adventure
Ultimatly all of the products are great, I just don't use all of the info. Furthermore one of the absolutly GREAT things about 3rd ed, is that the expanded rules are usually a couple of pages, just enough to explain a new concept. I.e. Corruption, or Disease etc.
If you are planing on running this version for the long haul, I would recomend purchasing everything if you can. It all has great fluff and is valuable. The players guide does have improved explinations of rules and an "INDEX" which helps alot but is not at all mandatory. If it came down to purchasing one of the Chaos God expansions or The players guide, skip the players guide.
Basically I would by the Hard Back books absolutly last, even after all of the POD expansion.
Just my 2 cents. Hope this helps