It doesn't matter if you have IPS panel or not, it is the light (CCF) in the panel that fades with time regardless. Every week is a bit of a stretch, but if you want the best quality, calibration on a regular basis is important, since only LED LCD's maintain their brightness over their life time.
A 32bit system cannot use 4GBs of RAM (3.5GB Max), so there is little point in getting that much if you stay 32bit. As noted, any Core 2 Duo system will be more than enough, unless you do tons of batch converting and mass exporting all day. The only reason to go for a Core i3, Core i5 or Core i7 system is if you also work with video a lot, which takes more horsepower. The GPU can matter if you work with high resolution external monitors, but most mobile GPUs can handle multiple monitor setups without any trouble.