So, my recommendation is to restrict the spells like 5e says to so wizards can't use Bonus Actions and Action Spells in the same round, and so Clerics can't cast both Cure Wounds and Healing Word in the same round.
Disagree with this!!!!! I love being able to cast misty step + a damage spell or a healing spell + a damage spell.
You won't love it later when an evil lich or higher level cleric turns the tables on you. Well, at least I imagine you won't. It's all fun and games when YOU are the one with the OP abilities. It's not so fun when it's your enemy turning it against you. High volatility is what causes combat encounters to become quickly VERY unfun.
Imagine a boss like the Hag only with the ability to cast Fireball or Lightning Bolt, or both. Wins initiative. Casts Fireball at your mage and entire party. Your spellcaster at Level 5 will likely only have about 30ish HP. One Fireball is 8d6 damage. Average Damage is 24. In one round, your mage is almost dead, as is half your party.
But then, just to be a butt, she casts Misty Step to teleport 30 feet away and then runs 30 feet to position herself behind total cover. Thus, you aren't able to even hit her on your turn because she was able to Fireball you and teleport and run around a corner so you don't have line of sight. You try your best to move into position. Round 2, comes out of hiding and Fireballs you again. Then teleports and runs around a corner again into hiding. THESE are the kinds of things I'm afraid of happening in later game. You can't give spellcasters such free reign or they will obliterate you later.
At low levels, 4 and under, spellcasters are weaker on purpose. It is to set the ground work for later levels. The issue, Icelyn, is that when you leave spellcasters less limited at lower levels, when they reach higher levels, those lack of restrictions suddenly turn into REALLY OP abilities. I'm telling you, wizards and other spellcasters are going to become insanely terrible at higher levels, turning all other classes into obsolete nobodies. Either that, or they're going to have to REALLY create a ton of MORE insane homebrew for the other classes to offset the spellcasters' insane spellcasting abilities.
