Spellcasters should be familiar with their own spells (another advantage of starting low level), and the resolution of most situations uses simple d20 mechanics/advantage/constested rolls. It's not a particularly rules-dense system.
Your biggest concern is keeping the encounters and challenges interesting and not letting them bog down. Don't get the party stuck in a Big Fight against monsters that are too samey or lack pizazz. A big pack of ogres might be a challenge, but it's a boring fucking challenge unless you give some of the ogres some weird attacks or behaviors.
If you're going into the 4th round of a fight, you better have a plan for something interesting to happen in the 4th to keep everyone's attention focused, be it environmental, some 3rd party monster showing up and attacking both sides, or some other crazy development.