If a creature had resistance to spells, and then cast fire resistance on it, would it take only 1/4 damage from all fire spells?
Nope, they don't stack.
Page 197 of the PHB:
Multiple instances of resistance or vulnerability that affect the same damage type count as only one instance. For example, if a creature has resistance to fire damage as well as resistance to all nonmagical damage, the damage of nonmagical fire is reduced by half against the creature, not reduced by three-quarters.