You didn’t pick an easy one to start with! This is an old kit (37yrs!) and while it has some features that are better than Trumpeter’s, it has a lot of failings, commensurate with the time it was issued.
The first is that it compromises accuracy for “working” parts. A spinning prop is one thing, relying on styrene hinges is another. I’d suggest that if you want the working undercarriage, then be prepared to live with a little inaccuracy in the wheel well, which, by the way, isn’t boxed in. You have to do that. Or, if you have a Trumpeter Spitfire Floatplane, you can use the spare wheel wells provided with that. Then, you just need to sand it down to fit the wing, and add a piece of thin plastic card, curved over the strut part of the well.
The next thing you should do is paint the engine satin black (just thought I’d get in quick with that one). There are quite a few details missing from the engine bay. If you’d rather build this one not showing the engine, then you’ll save yourself a lot of time and anguish, because the engine panels are inaccurate on the inside, as well, but look fine if cemented in place. Alternatively, you could just cement the side panels and have a “top down” view of the Merlin.
The cockpit is actually pretty good. The seat is much more accurate thatn Trumpeter’s but if you don’t have the pilot sitting in it, then you’ll need to make yourself some harnesses etc. I’m currently making one, and I have the pilot sitting in it:
When it comes back to the wing, the machine guns can be exposed. They aren’t as detailed as the ones in the Trumpeter, or the later Airfix Hurricane. Please yourself if you want the bays open or not, but if you open them, then you let yourself in for a bit of scratchbuilding the gun bay interior structure, which comprises a forward solid face (the rear of the wing spar box) and trusses down either side, and a solid face at the rear. Similarly, for the ammo box bays. Or you could ignore it.
Here is a pic of the gun bay, courtesy of Edgar Brooks:
The battery doesn’t sit on the fuselage floor. It sits on a "shelf " behind the oxygen bottles. The square hatch on the port side (beneath the clear navigation light on the top of the fuselgage) is the radio access hatch. I found that it easier to remove the straps on those bottles, by the way, and replace them with strips of card, than to ignore the moulded detail.
That should get your started, anyway.
Have fun,
Bruce