Any machine for £200 will have way more power than you need for what you do. Processing power has become so cheap, it is not like the old days where a computer becomes 'out of date' after a few years.
Anything more is an extra.
An SSD hard drive will result in fast boot times, and slightly faster loading times (though you won't notice this if you don't play games).
4gb memory is all you need, sure get more if you have the cash, but if you are on a budget stick to what you need.
Windows 7 is best, but if you go shop bought you are tied into what windows licenses they have.