They will put all the weapons and vehicles of the halo past including halo wars 2 ?.I don’t know the exactly response for you but, the Banished Red color is the same of Halo Wars 2 (Brute)
With all that it would be the halo never seen before.
What if the banished can be given a different color like red and gray?
From the recent Ask343 event: https://www.youtube.com/watch?v=UYlRabRA82U&t=52s
, it's strongly hinted that a number of legacy weapons as well as new weapons will be there, if not at launch then in the future. Likewise, though, they're being very clear that they want a clean sandbox in terms of avoiding having too many weapons with overlapping roles (which, let's face it, Halo unfortunately does have). Will be very interesting to hear.
The latter point I've seen nothing on, but given the coatings for weapons my guess would be most items and armours can probably have them applied.