Toxic Deluge is likely a little more reliable than Dead of Winter, unless you are dedicated to Astrolabe and a higher than normal SC-Swamp count. I also like
Marsh Casualties and
Darkblast for sweepers/repeatable removal.
Honestly, Plague Engineer is good enough to be a maindeck card in Pox. It does everything you want, it just doesn't play well with Smallpox/Innocent Blood if he's you're only creature on board. I would want to go deep with it though, with something like
Unearth to provide some card draw and combos with Plague Engineer post-Smallpox/blocking.
As for PW's, it's one of the few ways that Pox really can't interact outside of combat (which is usually not enough with anemic threats like Bloodghast, Factory.) Bitterblossom is really good at pressuring planeswalkers, but I wouldn't leave home without some number of Pithing Needle in my sideboard, likely 3.