Going down the custom keyboard rabbit hole can be quite daunting, And expensive...
But the good thing is, is that it doesn't have to be. I guess it depends if you want features like Stuff the Wooting keyboards provide then your options do shrink, but there are some REALLY good keyboards Out there which won't break the bank and are just miles better than anything all the mainstream keyboard manufacturers like Corsair, Asus, Razer offer at a lower price, in terms of build quality and feel.
Considering you're coming from a K63, If you wanted to stay with the TKL lay out, I'd check out the MonsGeek M3W, just over £100 at the moment, trimode, rgb and all that good stuff. If you're willing to go down to 75% which I personally think is a wonderful sweet spot then the options open up even more.