I used to paint and airbrush car and motorcycle related things but that was in urethanes. I use that same 3M mask but with a different organic vapor cartridge. I don't think you would need the P100 level stuff. I love that mask, its very comfortable and breathes really easily. Another thing to keep in mind is those cartridges expire quickly, like within a month or so. You can prolong it a bit by keeping them in air tight ziplock bags but really they're designed to be rotated often.
I think theres actually a good point to TP4's comment about getting something thats better than nothing but not really required to go all out. What you're spraying with models isnt nearly as damaging as some of the stuff you use in the automotive industry. I think getting some general airflow through the "booth" you'll be spraying in is the more important investment. Get that right, and you probably are safe with a few painting sessions with just a simple dust mask to keep paint out.