#4 All the way.
Rig either an antenna, a car, or a barrel with C4 and approach from the opposite direction. If you are close to being discovered, blow em up. You can put down several C4 and blow them.
Don't rely on the auto assignment of staff and extract, extract, extract. The mission targest and sometimes their bodyguards have amazing stats.
Get a MG:GZ 100% savegame and upload/download, you get incredibly good personal very early.
Don't waste too many recources on main weapons. Trank gun and silenced assault rifle will do for a very long time along with a third weapon of choice (sniper or rpg). Concentrate on equipment.
TRY THE DECOY! I ambushed a whole tank battalion with one decoy.
BACKUP your savegame files. Strangely, they are (at least on my machine) in the Ground Zeroes folder
Steam/userdata/#youraccount#/311340/remote
311340 is the GZ ID number, not the TPP ID number...
[Edited by madatcheats, 9/3/2015 3:10:04 AM]
Great tip on the MG:GZ, I did import my own, but it wasn't anywhere near 100%.
I'll go grab a 100% save and import
As for the decoy, I don't have it yet, as I've unfortunatly not been able to play as much yet, but great tip. I'll make sure to test that out