I essentially try to do what I can in each event. I am not wiling to buy resources so I do not spend money on them.....ever. The current Van Helsing event I think I can complete as I gained a massive amount of ironite from the sac event (I spent a load of gold - around 120m in BoS not sure on vortexes achieved but went from 90 Alchemist frags up to 570!). But that is all fine - I gained loads of missing characters through the last few events and what you could get from them....not sure when Gunner Mino will be mine but not soon it seems!
I have managed to complete Raven, Airstrip to get the characters as well as one Mayan....I can only really do this as I can play nearly all day.
The Dracula event is a monster for sure - it is the longest grind but as I get zero luck in event souls it is what I have to do get the characters......I have all but VH and Gunner Wolf so far but they all came from Halloween souls, sac event etc
Still no easy way to get Lucifer or Dark Lilith as had no way to get them in events so that will just need to be long term. I have a maxed WLOL and a Raven Alter character and several others in various stages so again that will just take time and grinding so they can add to the collection.