I would like your opinions on things such as: what makes a good server;
What makes a good server? The community. A close-knit, fun-loving community who enjoy getting on each and every day is what makes a good server.
What makes a good spawn area? A spawn area, in my opinion, is something that catches the eye of new players, helps them get started on your server(with information and maybe even some basic tools), and is interesting enough to keep players coming to it even after they move away from it.
how many mod to player ratio should there be and other things like that.
How many mods to player ratio? Kind of hard to say, some people can handle more people than others. I'd say stick to a 20-25:1 ratio. It may seem like not much but that allows your players to feel like there is always someone to help them and it still takes a load off your shoulders.
Also what's a good slot amount to start with?
Depends on your server, I'd say 20-25 on average. You can adjust depending on your server specs.
and other things like that.
Make a website(either yourself or through a website hosting service) that catches the players' eye and makes them want to visit it again. I like to use dynamic maps, even though they can eat up quite a bit of RAM if not set up properly, since it allows players to see their progress from a different perspective. One more thing I like to do is create a forum that has plenty of topics for players to discuss. Topics might range from tutorials, to a gallery to show off their builds, and maybe a place to talk about non-minecraft related stuff.
Source: A long history in servers and customer support.
