To be honest I think the survivors scenario would be the easiest to survive in. A fast due off would leave a lot if infrastruscture and resources available. If you got organised and started scavenging quickly you could cover yourself for a year or two without needing to farm much. So for me defence and water would be top priority in a location. I would go for a smallish building, isolated with a well adjacent and preferably inside a good perimeter. Sieges are nothing new and were generally successful when the defenders ran out of food, water or suffered disease.
So im guessing a small farm but it must have a well. Scavenging priorities would be a big trailer and vehicle if necessary, general prepper food, medical supplies, bottled water or large containers and fill from the well and store inside, weapons any and all and ammunition, equipment and building materials. Other survivors, thus is by far the hardest as each contact is a risk, I would avoid groups all together initially as alliances will already have been made. I'm not saying to turn away people but trust your gut. If I felt a single flutter id be gone
Lie low for as long as possible, if no one knows your there you might avoid all the trouble. Don't just attack anyone who comes near but don't trust them either. As a rule clean well presented people and mixed sex groups (with the women acting as equals) are probably less of a threat. It's useful to think of this the other way round too, when your out scavenging, announce your presence every time you approach a building, don't enter if it appears in use.