I know it’s not ideal but curious if Font of Magic be used the “free” castings of guiding bolt that Stars Druid gives you. Could be an interesting dip. You get:

light and medium Armor with shields

Cantrips and level 1 spells you can’t cast

Stary forms that work off of proficiency bonus

Free Guiding bolt prepared and casting

free guidance 

Could be interesting. Upcast spells in those higher spell slots. Could it be something? 

The free castings of guiding bolt are cast at base level without using spell slot. Nothing changes that. So, Font of Magic would not provide any interaction. All Font of Magic does is change sorc points into spell slots or vice versa. The free guiding bolts don't use spell slots at all.

You can't upcast the spells if they don't use spell slots. Without a spell slot they can only be cast at base level unless the feature specifies otherwise.