Good stuff on the cannon stubs, although on a preserved aircraft, it's often difficult to know what is, and what isn't, original equipment fit, or restored to 'representative'. I know of MkIXs which have been around for many years lacking both the cannon fairing and stub, and then have been restored to 'standard' appearance, with both being retro-fitted, as the 'warbird' community bring aircraft back to full WW2 appearance. I'm not wholly doubting the lack of the stub, but to date, this is the first I've heard, or seen of it.
The alternative wing tips on the ICM kit have caused the problem here - the 'clipped' tip fits OK, but the extended tip, and standard tip, need the gap filling, and you'll probably find that there's a 'step' between the tip and the wing, which will need building-up with filler and blending to achieve a smooth transition from wing to tip.
Note that on the real aircraft, the wing tip joint was covered by a visible, narrow, thin metal strip which, when removed, allowed access to the retaining bolts.
There were variations on the colour of the wheel well and inside of the door. The inner face of the door was normally painted the same colour as the underside, as were the side 'walls' of the wheel well, with the 'roof' in the interior Cockpit Grey Green colour, although there were of course exceptions, when the 'roof' was also the underside colour. Variations included door in the underside colour, and the entire wheel well in grey green.
The gear legs were normally finished in 'Aluminium', a paint mixed from clear dope and aluminium powder, giving a slightly greyish silver appearance.