putting 4 Noctua NF F12s might get some better temps with the H220, considering the extra static pressure compared to the stock fans. In my experience, it doesn't take much extra static pressure to get better temps. Adding a GPU, later on, to a H220 loop might be pointless considering the radiator thickness, unless you live in the northpole. but it kinda rules out the h220. I'd still go for the H100i. As for proper watercooling. You could get an XSPC watercooling kit for £140.
Getting some NF F12s in there will help noise, static pressure (only slightly) and temps (slightly 1-2 degrees give or take). but it'll up your overall cost by about £30.
So £100 for the h100i (or something like that)
£140 for the wc kit, plus £30 for the nf f12s. Ohh, don't forget coolant!
I'd say you could have temps at the max 8-9 degress better with the wc kit than the h100i, but it's your opinion if you think that extra £70 is worth it.