I built a 3" Madcow Sport-X (
https://www.madcowrocketry.com/3-sport-x/ ) for my level 1, launched with a Aerotech H283 DMS motor with a Chute Release. The OpenRocket sim said 2303 ft and 402 mph. I wanted to get the rocket off the rail with good speed and accomplished that quite well. Another rocket that I have since built in this same size range is the Loc/Precision Athena (
https://locprecision.com/product/athena3/ ). The split fins weren't really any harder to build, just took more time. It has a 29mm MMT which makes it cheap to fly with Aerotech DMS motors. I plan to fly it this weekend on the Aerotech H182R DMS motor.
Things I wouldn't change
I didn't want to go the low and slow route. I figured that the 3" rocket hit a sweet spot for how I wanted to fly Level 1 motors and the high power fields and waivers for my club support going a bit higher/faster.
I would use the Chute Release again. I had flown it several times in mid power rockets and was comfortable with packing a chute with it. It also let me use a larger than normal chute without having to worry about drift. Even though the Sport-X fins are a good shape to prevent landing damage, I still wanted that extra insurance.
I would definitely go with a DMS motor again - less fuss for a launch that I was already nervous about.
Things I would change
I didn't have a preflight checklist written down. The launch still went ok but I now have a checklist that I keep in a binder that I follow before launching. I am starting to get into electronic deployment and have a separate checklist for that. I will also step through that list prior to leaving for a launch. It helps me to know that I have everything with me that I'll need for the day, which leads to...
I didn't have a dedicated range box when I did my Level 1. I scrambled to get everything I thought I would need gathered up and that added extra stress. I now have a dedicated range box with the tools and supplies I need, and some for just in case.
Bring somebody along to take photos. I thought I would snap a few pictures but decided to focus on just getting the rocket ready. I have a few photos from other club members but wish I had a few more.
And finally, I left my wallet at home the day of my launch. Not sure if that was good or bad, but it did keep me from buying out the inventory of our motor vendor.
At the end of it all, build and fly the rocket that makes him happy. If it is a minimum diameter screamer, go for it. If it is a 4", 5.5", or 7.5" low and slow - great. Just make sure you have the field and waiver to support what you are doing, find a mentor if you are doing something completely new (since you already have your CAR Level 3, that is you), and have fun. This is what I am doing with my son right now. He really liked the looks of the Loc/Precision 4" T-Loc and wants to get his Jr Level 1 with a H115DM DMS motor. He just finished his first set of fin fillets on it (they look better than what I can usually lay down) and will start painting it this weekend.