I used the following guides from TimeTravelKiwi, these were not made by me so take no credit for them. They have timestamps to jump to specific tasks.https://www.youtube.com/playlist?list=PL8yMIdgUrjkOSAouvJs1m...
I personally completed all missions, then s ranked them all and now doing mission tasks.
By this time you can have the infinity bandana giving you infinite ammo and suppressor - found in development>Weapons/Items>uniform
You can also develop Stealth Camo.PP and Stealth Camo. One recharges automatically but while recharging you can use the limited use one then switch back. You can run into bases and nobody sees you. - found in development>Weapons/Items>items
Finally, once you have all mission tasks just chose return to ACC in menu, you dont need to exfiltrate hot zone or complete mission.
Any questions just ask.