there is a rooftop garden nearby where you can find some flying pokemon
btw dont fear! i made the exact same mistake when i started, i believe with mudkip/marshtomp and trubbish ^^
you can find ghastly around the wastelands, it has been answered somewhere earlier in this thread, about the poison gym, uh i suggest you bring a pokemon that learns eartquake early on since its 2v2
i dont have a map, but at some point you have to sneak infront of a tree, if you are past the tree you have to jump down a ledge.
hope this helps
after you saved cain you can just walk north-west and get back to the boat