My inclination, having done the IR in the USA, is to treat the US option as a device for completing the "IR project" and not as some open ended adventure where you learn to fly on instruments.
For a VFR-only pilot, instrument flight is usually quite hard to start with. A monkey can learn to fly straight and level in IMC, but doing other stuff at the same time quickly reaches the brain capacity. I would recommend getting through this stage in the UK first and not going to the USA until one more or less knows what one should be doing. The US is not the place to be doing ground school type of stuff. Then the 2-3wks spent there is mostly a "consolidation" thing, but, trust me, it won't be a walkover.