Citadel's plastic glue is OK, but Revell Contacta Pro has a stronger bond and is cheaper. I would also keep a lighter handy, both Citadel and Revell's small metal nozzle gets clogged, a quick flamer purge clears it
Rustoleum is great for priming that 2 time coverage just works. It works against it if you want to preshade though.
Citadel Moldline Remover... Nice option to have, not really required, I have one, but most of the time I just use the blunt edge on the clippers.
Files, I would say are not need in getting started with the hobby, when you get into conversions and forgeworld kit, then yeah, super handy to have.