I always wanted to have to play a Hedgewitch who had a broad magic with a large number of first level spells and breaks some of the rules of magic. Its a Land Druid 2, Divination Wizard 2, Life Cleric 1, Land Druid 3+. The idea is he has heavy armor, wizard, cleric and druid spells which allows him to do lots of different types of magic with multiple ritual casting spells. With all of the subclass features he will be better at getting spells back from short rests, better healing from each spell, divination dice and the most flexible spell slots.
I think it would be fun as either the only magic user or as a backup magic user to fill all needs and niches.
I recommend you give the players a Bag of Beans. Its a chaos machine and a great method to get your players to do something fun without completely derailing the campaign. We all really enjoy the pink toads (random monsters) since you can just roll up something crazy and do a combat.
We had the mummy lord come up which ended up being a huge plot point after they let it sit for a while. It changed the course of what we wanted to play in a fun way.