Well you are welcome, and im just happy to help.
Certainly some options for once you have bought the PC, as they are all seperate. And by 'upgrading the internet speed', I interpret it to mean a faster / better quality conection via your Internet Service Provider.
There are 2 important factors to know about chosing one - consistency of delivery of service (ie do they 'traffic shape' to limit your servive at particular times of the day to suit them), and 'capping' (setting a limit on the amount you can use in a given month). Its become common practice for many ISPs to state 'unlimitted data' because it looks good for their potential new customers, however most will then have "(fair use)" or similar in small lettering, which means that firstly its not unlimited, and secondly since they dont say what that fair use is, the customer is at the mercy of the large (sometimes multinational) organising being fair themselves
Fortunately there is one very simple solution. Ask around here for opinions, then read
http://www.thinkbroadband.com/ , and after that do what i did - subscribe to "
Be".
After all that, you could even treat your significant other to a new router (the ISP will provide one, but its cheap and basic) - wont improve the speeds, but a good router can do wonders for features and control. Post back here as and when needed.
Enjoy!
Edit: One more thought. You said earlier about buying 2 x 1TB drives for inside the PC, which you would RAID (in RAID 1 mirroring) for data security - not a bad idea. However if you are considering a NAS, this would do much of this. I have a NAS (if you have far too much time you can follow the link in my signature to read my discoveries and exploits), and again can give some advice, ideas and principles.
Also, and i'm surprised that i've not thought of mentioning this before now, but what ideas do you have for 3 very important 'peripherals' - mouse, keyboard and speakers? For your budget, i'd be looking to complement such a strong main PC with at least good quality peripherals since they are the main way of interacting with the PC.
Some ideas:
Speakers (I have these) Creative Gigaworks T40 series II (
review here)
£83.
Mouse: A tough call.
Have a browse here.
Keyboard: I am delighted with my own choice (again - but i do my research!).
Logitech illuminated. It's less 'flashy' and more 'classy / understated', and i love it. Very quiet too.
£61.