Complicated storylines ARE A GOOD THING
However the players don't need to deal with every aspect of the lore.
ideally you'd want like 100 pages of lore readily available but only 1 page is needed to function in the modern times and even less is needed to make a profile and get started.
"Do and be whatever you want" guilds are often unattractive to me, that's what you do before you join.
"the world is swallowed by darkness and they can't get inside" sounds to me like its a survival horror game so It doesn't really sound like were gonna be doing whatever we want... we can't even go outside without fighting something and risking something. Well outside the city I guess but even still much of the story will probably be dominated by the fact the world is more or less ending. This could actually be very suffocating to the creative process for those getting started especially without a lot of lore when the premise basically makes you a graduate of a school you currently know nothing about and probably didn't know much about even if you roleplayed here once, I for one never figured out much about it.
When it comes down to it, rich lore and an easy getting started process is the answer to a lot of your problems but then do you really intend to turn Asworth into what could potentially turn into a survival horror thing? Even if you say they can't get into the school or city you're gonna have to do one of the following
1. never actually let the main antagonistic force into the city causing those within to be focused on them and have to learn to and go interact with them causing it to be a survival horror thing
or
2. let them in causing it to be a survival horror thing regardless.
Basically this is going to become a combat heavy thing that will turn many off and away but it may attract some types..
Not saying this is bad but is this what you imagined the average character would be like


because this will make sense with what you've got so far. Would this really be a good place for Wizard squirrels? Yes or no is fine but choose early