Here is yet another idea about multiple actions per turn.
A martial character could attack 2 enemies at 5th level and 3 enemies at 10th level and trade one action for a reaction out of turn.
A caster character would get 1 action or 1 reaction spell at 1st through 4th level and 1 action and 1 reaction at 5th level and 10th level but the damage from the spell or the severity of the damage conditions would increase with level. All spells would then be encounter spells and could only be cast 1 time during a fight.
A martial character could attack 2 enemies at 5th level and 3 enemies at 10th level and trade one action for a reaction out of turn.
A caster character would get 1 action or 1 reaction spell at 1st through 4th level and 1 action and 1 reaction at 5th level and 10th level but the damage from the spell or the severity of the damage conditions would increase with level. All spells would then be encounter spells and could only be cast 1 time during a fight.