You made some good picks and some bad ones.
First of all, the fisher-price watercooling will get beaten, hands down, by a good air cooler. Something like a Hyper 212+ with a pair of aftermarket fans is going to be still small, but will cool nearly as well for a fraction of the price... and be a million times more reliable. If you computer can handle a bigger cooler, a Noctua -D14 will easily outperform an H100i for less money, while still being miles more reliable.
If you can, upgrade the motherboard - MSI isn't known for amazing stuff, and if you want to be doing a lot of overclocking, you need a good motherboard. Has AsRock gotten any easier to find in the UK yet?
Last note:
Bad, bad, bad pick on the power supply. You don't need more than 550w, and you want a RELIABLE power supply. That is neither, probably can't actually produce even 700w peak, and is likely to explode, catch on fire, or fry your components. Use common sense - a 750w power supply that's actually able to give 750w is going to be more than £60. Go with a lower rated power supply, because you don't need 750w anyways, and get one that's actually good, instead of a ticking wallet-bomb.