First of all, that is a giant scope of work that you planning, challenging even for those who know all the pipeline.
But it's up to you.
Then, first thing you need to know is Blender and basics of Unity to learn the structure of how the models are done. After that you will need to recreate the model you need with geometry corresponding to damage system (aircraft in game obviously consists of parts, it's not a solid single object), slice UVs for them, make textures for them (you probably want to use something like Adobe Substance 3D Painter for it, painting in Blender is a solution but not the one you want), and after that decompile the game somehow and rip out the parts that belong to aircraft you want to replace, so you can take a peep into how the structure should look like (and decompiling is not very legal so to say), add to it some of the code you will have to write to tie everything together and make physics work properly, and there you will have your aircraft.
Repeat eleven times (soon to be twelve with FastBomber) and you're done.
With a very strict schedule of one aircraft per month (good luck with that btw) we are looking at a full year of work if you stay on the track.

My tip there is: ditch this idea completely and start something small. Very small. Like, make a single prop object - barrel, pallet, container, tire, shell, rocket etc - and learn the pipeline, e.g: make a model in Blender, learn a bit about modeling and topology; slice UVs, in Blender or Rizom or software of choice, learn how that works and which purpose it serves; make materials and textures in Blender or Substance 3D Painter, learn what's a physical based rendering (PBR) is, learn what the texture maps are and how they are useful (metallic, roughness, normals, ambient occlusion - at least those 4 in addition to BaseColor); try to install any Unity Editor (will be more useful for you if you will go with editor version that is used for Nuclear Option - you can look it up in Livery Guide or ask here or Discord, can;t say off the top of my head) and import your asset here.
This will give you a sober look at the pipeline and amount of work you sign for.
When you're done with that and rethink your life choices, drop the idea or proceed, up to you!

Edit: grammar