Yes you can fit the ivybridge i5 but with that board i'd recommend the i5-3470, cause you wont be able to oc the i5-3570k
You'll need to flash the board see this :
Update BIOS for IvyBridge 22nm CPU.
- Update VBIOS version.
- Update USB module.
- Improved memory compatibility.http://www.msi.com/product/mb/H61M-E23--B3-.html#/?div=BIOS
And the 7950 will do with that psu (it has a single rail +12v 55a 600w and with 2xpci-e connectors).