My humble advice:
proceed as you suggested, offering on Steam each different route as a separate DLC. Then, to tempt people to buy the full game, offer some discounted bundle with all routes together.
Then, on your site, offer only the (discounted) complete game with all the routes. Of course, if you can, implement the possibility to purchase routes separately on your site as well: but, if this is too technically difficult for you, I am sure people will understand, and buy it on Steam eventually
Anything not related to one of my specific games, like general polls or promo/sale announcements. For general talk about games, go to the Golden Lion subforum