Well, as a fellow server creator I started my journey on minehut and now have fully managed a server. (its been a but since I worked on it but I've been busy)
Overall things like different plugins and even some customs skripts that just round the playing experience and add a little more detail in benefit seem to work fine for player retention.
*psst* more about my journey: What are the biggest challenges you faced when starting out as a server owner, and how did you overcome them? (planetminecraft.com)

I'd say some sort of automated grief prevention is a must.

If youre running spigot or paper you can get some great plugins, you may be surprised how many people may visit - not all with good intentions

i think smp server are mainly succesful if they are form around a specific active community kinda like how mcmedon here on planetminecraft has a cool smp that many people enjoy play