I refinished some of the woodwork in my 1998 Contessa. Mine was all done with a clear finish on Alder, which was stained slightly on the cabinet frames but not on the doors. I covered the bedroom TV opening with a pair of doors that I made out of new Alder and finished with a clear, oil based wipe-on varnish (see below). My existing cabinetry in the front cabin had some battering that I repaired, and I used a stain to match the surrounding wood and a water base wipe-on varnish to finish (see below).
Due to the original finish being more than 2 years old, it is unlikely that you will encounter a chemical compatibility problem. In any case, you should do a test piece somewhere where any lifting of the old finish, when you put on the new, will not show. Assuming compatibility, sand lightly with 220 or finer grit paper and apply whatever you have chosen.
To add new wood and match the existing colours, you will need to stain, as the existing wood has been exposed to several years of UV that has likely darkened it somewhat. If you are prepared to wait without staining, for the UV darkening to affect the new wood, within a couple of years you won't notice the difference, and within 5 years you won't be able to tell which is the new wood, from the colour alone.
For ease of getting a good finish, I prefer the Minwax wiping varnish, in an oil base. I have tried the water based product, but find that it dries too fast and leaves a streaky finish. The oil base gives you time to wipe it smooth and leaves a nice, semi-gloss finish very much like the original finish. The added advantage is that this is a very thin finish, per coat, so you don't get a buildup that would affect the colour of the wood.
If you are set up for and experienced in spraying (if that was the case you wouldn't be posting here) a good spray lacquer finish is likely just what the factory did, and for mass production of a great finish, it is the best.
If your coach was done in high gloss, you will need to apply a high gloss, interior varnish. Exterior varnishes are tougher, but also contain UV inhibitors, which will darken the finish quite a bit, so is undesireable for your purposes.