Although your PSU isn't ideal, you should be ok with nothing more than a 4->8-pin adaptor to save on cash (I think, with the options and budget your working with, you want to be saving cash for the good stuff).
Ignoring your request for request for Christmas delivery (realistically it'll be Christmas Eve before an order is dispatched unfortunately), if it was my £350 I think I'd look on eBay for a second hand i5 3rd generation (or even a 3770k if budget allows) / motherboard. The problem is that Socket 1155 is "dead" so it seems counter productive to sink too much cash in, but if you go for the Haswell socket then you end up spending quite a lot more on the motherboard and get little real performance improvement.
Memory is a tough one - it's very expensive right now, but for a gaming PC all you *need* is 8GB. But for a day-to-day PC, I wouldn't want less than 16GB...
(as always, my opinion != the best advice)