I like the idea of a three part scenario but would probably do it over a few weeks to allow for other projects/gaming. That way you could bring different scenery each game.
To make it easier, for me,

i might leave the GW as level 4 Hero with T-D ... BUT ... look to summoning the Minor Demonic Pact (Melee +2/Will +1/Hits 2 etc). The Baby Demon has less "Oomph!" but still has a bit of a bite*.
I could spend the 55 pts saved by making the GW a Werewolf (lose an unarmed Minion too) or a Punk with a High Velocity Rifle! Be careful what you wish for

Consider taking an Exorcist Judge ...
*That or stop taking the Class II with Wings/Lightning Bolt which gives me a couple of extra cannon-fodder