The restoration skill is automatically added when the difficulty level is set to Story, regardless of location. Reverting to the Fort Joy save would allow you to get additional skill books, and either make your current builds more effective, or give you the option to respec and have appropriate skills and equipment available.
If the lower difficulty level lets you get through the Lady Vengeance fight, you could check out the start of the next act and see if you can get new skillbooks there. When you start getting the hang of the skill system, etc, you can increase the difficulty back to Explorer.
It isn't bad having only one magic user, though at least on higher difficulties a lot of people prefer going all physical damage, all magical or two characters focusing on each. One magic user is ok on lower difficulties (even if focusing on healing, teleportation, crowd control, etc, more than damage), and a ranger can help with magic damage using elemental arrows, etc.
There should be some skill guides online, along with character guides (with contradictory opinions on what works best, but you just need a general idea of what skills you would like to get and how to use them).
If you want to change companion characters, as opposed to respecing, you must do so before continuing on the Lady Vengeance; after the fight there they will no longer be available, and the companions in the party in the next act will be permanently linked to the avatar that (re)recruited them on the Lady Vengeance (only relevant in multiplayer).
Personally, I'd only suggest starting over if you have an idea of what you would do differently with building the party, and preferably some quests, etc, you'd like to do differently.
I'm not sure if there is as much of a multiplayer component for the Switch version as on PC (especially with it requiring Nintendo's extra Online service), but if possible, it might help if you can arrange a multiplayer game with someone willing to give some advice as you play. Playing the game from a different account would give a separate drive space for saves (though only the host can save).
