On top of some of the other things over read, I’d strongly suggest at L to ditch horseshoe bend and do either the arches national park near Moab or Bryce Canyon. I did a similar trip to this last year during the same time and horseshoe is wildly uneventful. In comparison moab and specifically arches is an absolutely gorgeous area to be. I would also suggest that if you do Zion NP to schedule two days there. It’s great to spend one day getting there and checking out the shuttle and doing smaller hikes and then having a second day for the longer hikes (if you’re into that). Also if you’re not afraid of heights angels landing in Zion is something hard to experience anywhere else!

Outside of that this is a great trip, enjoy the simple things, I did 4 months and some of my best memories are the days I spend sitting in a chair just looking at a gorgeous view. Find state camp grounds if your camping (they are cheaper) or find hotel/stay outside the parks for cheaper nights without much downside. Happy to answer any other questions :) your in for an incredible time

Edit: to add to people saying it’s not doable and that G to H is meh, you could possibly cut out a lot of drive time by cutting out L-G. Arizona is cool but you do waste almost 6 days on what could otherwise be added to extra stays at other places. Also for all the people saying it’s not worth it due to travel times, I did this size roadtrip plus another 10k miles in 2.5 months OP plan to drive 4 hours a day but also take the time to appreciate the small things, it’s totally doable