I wonder if using smaller colony map sizes would help encouraging travel? Move to different biomes, catch some pokemon, then move on?

That would work somewhat. Using the set up camp mod and such.

I'm more concerned about the inherent escalation that happens in rimworld. Day 1-10 has little to no raids with 1 melee raider in them. Day 40-60 has raids of 6 dudes with guns.

I'm currently doing rough difficulty with randy random. What storyteller and difficulty would work better?

Also, I wonder if creating a new pokedex for each run is too much since there are so many pokemon and the escalation factor is present. So far, I have limited myself to 3-stage pokemon that require no special items or conditions to evolve. What else could I do?

I think the best choice would be to have an ascetic that'll get a mood buff from having a ♥♥♥♥♥♥ room, after all, you don't want your wealth going up by even a bit, that would mean harder raids, and training a lot of pokémon that can haul so you won't lose any time with your only colonist.

In regards to food, you could get the Hunt For Me mod, then you also wouldn't lose time with sowing or hunting yourself, you also get the plus of having your pokémon level up while at it, but you still should probably plant a lot of Healroot and drugs. Not sure how hard it would be to do it, but having a go-juiced army of Beedrills seems like something not even 6 guys with guns could deal with.

Try to land somewhere that has a lot of different biomes around, at least for the first quadrum it wouldn't be a good idea to travel too often, it would be wasting the few safe days you get at the start and that you could be using to tame or train. Also, don't worry too much about your unevolved pokémon losing a few limbs while fighting, they'll grow back once they evolve.

If you want to take even more care of the wealth problem, just start mining into mountains so not even your walls will count for wealth, you also get the plus of not having to worry about sieges. You could also make your colonist unable to fight or crippled in a way that doesn't affect them too much, like not having an ear or having painless scars.

About the Set Up Camp mod, it's a great idea, but you could also set your max colony ammount to max and have colonies in 5 different biomes, rotating between them by killing everything you can in that area and moving to the next one until you get what you want, you wouldn't need to rebuild a new base every time and I'd guess that's an effective way to grind for pseudo-legendaries. I guess you could also use the Draftable Animals mod if you don't want to risk your colonist at all while fighting.