Drop the impulse in your sustainer main motor for next flight. Maybe even adapt down to a 24 mm D12-5. You will get all the excitement of staging, a little less mass in the tail which will help your stability (I see you are already overstable, but the lower mass will also get you off the rail a bit quicker), and a lower max altitude which should give you a shorter recovery walk. If all goes well on that flight, consider going back to your F motor for next run.
IMO first flights for stagers should be to prove successful complete flight profile, not go for maximum altitude,
Was thinking about Q Jet Ds on the outboards, but doesn’t look like they have a 0 delay. And they mass more than the Estes C6-0. They would still work and give you more “oomph” off the pad, but they are going to hang on board your sustainer longer after propellant burn out (more drag, less altitude, not necessarily a BAD thing for first flight. Lot of smoke, which is good!) problem is they will separate at a much higher altitude than a Zero delay outboard motor. Your main booster should separate pretty low, so that won’t be too hard to track, but the outboards may be a bit hard to find/recover if they are riding on D12-4s.
You will need a lot of eyes on the flight to track all 4 parts.
Hope you get 4 straight trails!
