I'd very much recommend following t phant's speedruns for each level to give you the quickest route to each objective while avoiding as much confrontation as possible. It's possible to complete some missions in around 5 minutes with these routes. The checkpoints are very generous even on authentic difficulty so the videos don't have to be followed flawlessly.
Mission 1 - San Celini Island
Mission 2 - Bitanti Village
Mission 3 - Regilino Viaduct
Mission 4 - Lorino Dockyard
Mission 5 - Abrunza Monastery
Mission 6 - Magazzeno Facility
Mission 7 - Giovi Fiorini Mansion
Mission 8 - Allagra Fortress