As for your air filter, you want to strike a balance between airflow and safety. So any OEM or name brand air filter will do. You could try a K&N oiled filter, but they’re a bit more maintenance, and you probably won’t get the huge return on extra power that you might expect. You’re not running a high-strung in-line 4cyl race bike, after all. But the more air an engine can get, the easier it’ll run. Especially at altitude.