There really isn't a ton of difference between the capabilities of the opposing C3 in the first and second war. They do have an additional interceptor wing as well as a helicopter wing as the main differences. Honestly more so than going in with a blueprint layout of what units can most easily win you the next war, I would look at it as an opportunity to learn the war engine better in a relatively relaxed setting. As you climb war levels the challenge will become greater and greater, and once you hit war level 3 other players come into play potentially, so it's important to try to have a decent grasp of the finer mechanics before you get to that point rather than just having an optimum setup to win the next conflict.
I might recommend actually saving up a little and building up your newly acquired country. When you feel that both it and your main country are financially ready, build a variety of a few unit types before your next C3 war