After thinking about this further, I am not 100% certain what pokemon I will use. If possible, it might be nice to use pokemon from Johto who evolve in Sinnoh.
I might also do what I've been doing in my current reruns of Pokemon games and doing a simi nuzlocke. Meaning I only catch the first pokemon in each route, but ignore the death rule. This allows me to play pokemon I don't normally use, like I did with Buneary in Isle of Armor and it became one of my favorite pokemon after hating it for years. Sometimes I may mark a certain type that I can also catch.