My advice would indeed be 'don't bother and keep it simple' but I've been doing this for a while so I'm probably stuck in a comfort zone and like to stick with what works.

Scooter motors, especially the 350W ones, pack a punch on 24V with the right reduction and axe arm/head design so might be worth starting off with that then looking at a 36V upgrade if you still want more power.
As for 36V controllers, there used to be a handy range called Victor 883s which would have been ideal but they're not made anymore. Perhaps the next best option (although needs shipped from America) is the RageBridge 2 controller. Unfortunately that's in the low-end three figure price bracket, but it would happily handle it (and could perhaps be an investment as a dual-motor controller for if you build something with a larger drive setup in future). There may also be some second-hand ones in the UK that could work out a bit cheaper. http://e0designs.com/products/ragebridge2/