Just make sure your soap you use has no lotions in it...it might cause a paint problem when painting called(fish eyes). Best advise anyone has ever gave me on building is to treat every part as if it were a model itself and take your time building is not a race to get done but a challenge to build the best one can at a given point of experience. I have been building for over 44 years and still learn something new all the time...only dumb questions are the ones not asked.
Welcome Ian....you have some of my favorites in your stash I'm a huge Johan model fan nice collection. I am into promos and promo restorations of the 60,70s cars and kits.
I never had the Challenger one but did have the Mustang...decent kit too. Model kits are meant to be built eventually...if I had them Id build them unless there not your kind of kit then Id trade them or?