Amen

It's not a wooden railroad car, but in 1998, my wife and I took the layers and layers of old paint off our circa-1910 siding-and-shingle house and repainted. We learned a lot in the process. To echo John and Fred:
Surface prep should be 90-95% of your time and effort. Scrape off flaking paint and sand the edges. Sand the weather checks out to the best of your judgement. Fill nail holes with putty, caulk before priming, etc.
Put as much linseed on the wood as it will soak in before priming. We used a 50-50 mix of boiled linseed and mineral spirits, but the other mixtures mentioned work just fine too.
By the best paint you can get your hands on, and try to keep the primer and top coat from the same manufacturer. Paints are formulated as systems these days, not as independent components. (We used Sherwin-Williams "SuperPaint" and have been very pleased with how it's holding up. Our neighbor's house, done around the same time without the obsessive prep and with lower-quality paint, already needs a repaint.)
In a situation like this, where there is probably oil primer is preferable. Like Fred said, these days latex topcoat is of equal longevity and quality as oil. (There's no problem using oil primer and latex topcoat.) Latex has a slight advantage of being more flexible, and to a certain extent "self-healing" with scratches. Oil has the advantage of wearing a bit better, and not "blocking" on windows and doors. The best compromise might be latex on the large surfaces of the sides and ends, and oil on the door and window frames. Or if one has a clear UV-inhibiting advantage, go for that.
More is not necessarily better. A single coat of primer and two top coats should do it.
Good luck.