Hi there,
You don't need a 2500k if you are not overclocking, but it's not much more then a 2500 so you could get it anyway. A 2600(k) might be better because your apps might benefit from the hyper threading, but I don't think it's worth a ~£100 price hike on the system.
Any P67 or Z68 motherboard should be fine, I would suggest a discrete GPU so you can support multiple monitors better in future. Anything should do though, doesn't have to be a good one!
Memory, yes prices are silly, you can get 8gb of (slow) RAM for £30 but I would pump for 1600 mhz 4gb sticks, get 2 see how you do, if you need more get another two.
Get enough RAM so you never hit swap file, if this is on an SSD it can cause the SSD to wear out.
SSD - it is somewhat better to run them with some free space, depends on the drive, but it does help. Still using 100gb out of a 128gb one should be fine. Would suggest a M4 since it's likely to REALLY speed up your experience, but to be honest any SSD will be seriously fast.
Get a ~1TB backup/data drive too if you need it, always a good idea to have a backup.
You will also need to budget for Windows 7, any version should be fine except the very cheapest, be sure to get a 64 bit version.
Finally take a look at the
scan value systems for some inspiration! Your boss might also prefer 3rd party warranty to roll-your-own with component warranties.
Hope this helps any questions post away there are plenty of people here who can help with something with this. Good luck.