After a couple days of experimentation I can now confirm that the spawn rates do not vary by difficulty, and they probably do not flee (I've observed gangsters apparently move to a waypoint by an escape off the map, stop, and then turn back. Never seen one actually move through it).

Some of those initial spawns are listed as "group" which tells me that some spawn in clumps of 2 or more. Given that I've seen most sometimes-spawn gangsters hang around in groups divisible by 2, and assuming that each group is 2 gangsters each, that's a maximum of 33 gangsters if they ALL spawn which does seem to match observations.

I can only assume the "guard" gangsters are the stationary ones who block doorways, moving to let you up to the apartment?

After some experimentation I now know that Overkill produces somewhere around 26-33 gangsters per spawn, which indicates that difficulty might not affect it.

How many gangsters are set to spawn on Rats Day 2, and how are they set to behave? Do they try to exit the map? Does difficulty affect the number of gangsters spawned?

What's the DoT of the GL40/Piglet's incendiary rounds? The wiki lists the burn time (5 seconds) but I've never seen any mention of how frequent the fire damage procs or how much damage it does each time.

Both of those refills completely drained my ammo.

I don't know how efficient the filling was, only that a secondary's 20 rounds from a combined (primary + secondary) pool of 80 filled a sentry to 56%.

Apparently the number of shields he spawns with is random? I can't be sure team-mates didn't frag them, but he spawned on a Hoxton Revenge today with an arc of the phlanx missing for a total of 7 shields.

Refilling an empty sentry with full primary and secondary drains both your ammo pools to zero, and fills the sentry to 100%.

Refilling a sentry with one empty weapon and one full weapon appears to only half-fill the sentry. With an empty 60-pool primary and full 20-pool secondary I was able to fill the sentry to 56%.

It might be helpful to list the maps Winters does and doesn't spawn on?

"He cannot spawn on any of the following maps: Any Harvest and Trustee Bank, Car Shop, GO Bank, Shadow Raid, Transports (except for Train), Rats Days 2 and 3, Watchdogs Day 2, Bomb: Forest, Golden Grin Casino, Hotline Miami Day 2, Hoxton Breakout Day 1, Election Day Day 2, Framing Frame Days 2 and 3, Four Stores, Mallcrasher, Meltdown, and Nightclub."
https://www.reddit.com/r/paydaytheheist/comments/3mlbif/when_does_captain_winters_spawn_is_he_deathwish/cvfwm5f

I'll find out how many shields spawn alongside him (and therefore the minimum amount of damage you need to do to make them retreat) as soon as I can.