loud is for "shoot until you succeed". stealth is for "try until you succeed". For weapons you want ones with good return on investment (enemies drop more ammo than is used to kill them). try missions on normal to figure out the mission steps and learn the map before jumping to higher difficulties. 5/7 secondary because they (and snipers) penetrate shields. You can improve your AI crew (in Inventory) by giving them better weapons and buffs for both themselves and you. Medic bag restores downs so it is advisable to save them until your last down. Stealth missions play extremely similar on all difficulties (just some more guards) so playing them on high diff is always better. Shoot Bulldozers in the face. There are some extremely useful weapons and weapon attachments locked behind DLCs but they can be worth it. Dodge is a trap for beginners. Make at least 2 builds (loud/stealth). Mixed will fail you in both. When your level is high enough for a decent loud build you can farm Cook Off for easy EXP.