I got caught out 1st time through and didn't have a recent enough save to go back to. Had to struggle through to the end with inadequate armour. 2nd time I took it up to that point and then backtracked to complete as many side missions as I could find. When I couldn't find any more I joined a faction (I joined Freedom). The missions then involve attacking and taking over posts held by the other side (Duty). Just don't join a faction too soon as it can make completing some missions difficult.