I'm probably not the guy to answer on gas type, or gas vs. fluxcore - haven't used anything but C25 and hardwire since I got my mm211, used it for about 6 months, then found a sweet deal on a complete mm252/dual running gear/2 bottles/30A spool gun for about $100 more than the basic 252 - I've since run about 40 pounds of s6 wire thru the 252. No fluxcore at all yet, considering c02/Lincoln outershield .045 for the heavier fab.
I don't do aluminum, I've set up the 30A for .035 hardwire and use it when the 15' gun won't reach. My LWS has 2 lb. spools of hardwire for $6, so it's not too painful to use compared to 44# spools in the machine.
This strictly from reading, no experience yet - fluxcore = most spatter, think "stick on a roll" - co2 medium, spatter (as you noted) somewhat controllable with a good machine - C25, least spatter, less penetration than co2, and colder. Push reportedly gets better penetration than pull, assuming you NEVER violate the "stay at the front of the puddle" rule.
All that is immaterial if you're gonna "throw it in the truck and go", because unless you also throw in a wind-proof tent, you only have ONE option out in the open unless it's a REALLY calm day. I solved this (temporarily, til next year when I'll get back to a 32x60 addition to the shop) by building a "tent room" in front of my overflowing garage - it's big enough to get either tractor or 3/4 of my backhoe inside, and tarps around the perimeter give me a quiet enough space during all but pretty stormy weather.
Only porosity I've had so far is a couple times when I should have turned the gas valve on BEFORE welding

I've built a heavy set of brush forks, a 6'x8'x2' brush bucket for the Case, beefed up the frame on a heavy duty (up to 1" material) 48" slip roll I found on CL, and a couple other medium sized projects in my "tent room" so far, with no problems doing it this way.
One secret I've found works for me - a toilet paper "wind sock" - I simply hang a 3 foot piece of TP (preferably un-used)

from the ceiling over my weld bench or project, and if it's moving more than just a lazy wave, I go do something else til the wind's died down enough - with all the tarps around my "man tent", it can be fairly breezy outside and I can still weld - just to be safe, I usually turn up the gas to maybe 25 cfh if the TP is moving at all.
Kinda got off topic a bit maybe - guess the gist of it is "you should ask someone who's been there" :confused3: - I've only been welding since '74 (NOT professionally), and mig only about a year so most guys here are 'way ahead of me... Steve