Ok, i found an i5-2400 with a 10$ diff with the 2300.
So the config will be :
Mobo : Gigabyte GA-H61M-S2H (rev. 1.2)
CPU : intel sandy-bridge I5-2400
Ram : 2x2Go ddr3 1333
GPU : ASUS GeForce GTX 470 ENGTX470 or a EVGA 560ti SOC or Sapphire 5850 Toxic Edition (I still hesitate since i've never bought an ATI GPU
PSU : OCZ ZT Series 650w
Monitor : Samsung 23'' B2330
Advices with ht eGPU ?