A buddy that I work for has several sizes of JD’s and Kubotas and bought a new Kubota M7060 with cab a few weeks ago, I used it one full day last week and liked it pretty well for a mid size tractor.
I wouldn’t think it would kill your oats, I have a Woods that is similar to your Firminator and I plant into living plots all the time with no problem.
I wouldn’t mix the clover in your 3 point spreader, use your 3 point for the big seed and spread the clover with a chest mounted/over the shoulder walking spreader.
I was in your shoes for a long time and finally bit the bullet and bought a 7’ Woods minimal till planter about 5 years ago, it has small and large seed boxes and works great. It cut my planting time by about 2/3rds and I get much better germination, my only regret is that I didn’t buy one many...