Benefits of N ownership relate to slightly cheaper insurance (no Premium Tax), and slightly cheaper maintenance (no star annual, and no Notice 75).
Disadvantages are in the form of trust fees and convoluted ownership structure.
Net-net, it is probably only worth it on more complex singles and twins. Not something to worry about on a C152.
To fly an N outside the UK is not possible on your UK-issued JAR licence. The FARs specifically require an FAA licence.
Instruction towards your IMC rating does count as approved instructional time towards your FAA IR. IMC experience counts similarly.
2D