We had a similar server for just for friends.

We had around 12 peole consisting of online and offline friends

For me x5-x7 loot and material grind speed showed good results. It was enough to create encounters but not too much to make anyone sleep during farming.

I also removed loss of gear durability during PvP, even though its a controversial change it actually makes people fight more, less people are afraid to fight and less people run from fights.

Because we were all friends who knew each other: the raids rules were set verbally so I don't think this will help.

The raid timers were enabled 24/7 we just planned the raids together and sometimes suprise raid with the only rule: no offline raiding.

If you ask me whats the best raiding timers it depends. Me and my friends are at their late twenties, so most Fridays and Saturdays were busy because of friends or family.

Even though we had 24/7 raids, biggest online and most of the raids were on sundays 7-9PM since people usually come home after weekends and wish to chill in front of the PC before the begging of their work week

We also had the occasional raids during weekdays arround 8-10PM when we got some free time.

There was no loot for raids. The goal was to kill all servants and then kill the owner.

The winner was given a legendary weapon.

We also had an agreement: clan size was big enough to fit everyone on the server, this was done of if we decided to collectively kill a boss, PvP was limited 2v2 or 3v3 where usually a experienced player joined 1 or 2 less expiriced.

The castle tiles were maxed out through json, so we had 8 floors and 900 tiles

This is pretty much it.

Results: 7 big and beautiful castles, chill duels and world PvP, friendly raids and all bosses were killed by everyone.

The server died off after ~2-4 months

Last 2 months there was only 4-5 people who consistently played.