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Do you mean properly turn over, breaking up clumps, pick out all weeds/existing grass and roots etc? I did that for the raised beds section (maybe 25% of the total lawn area) and it was a good workout for me. If I want to get this done in the time remaining, hiring a machine to do some of it for me seems like a wise move - remembering that you are a globally successful endurance athlete in your physical prime and I am a sedentary office drone at least 10 years older than you, I'm not sure our ideas of 'a good workout' will closely align 🤣
No need to rotivate. Just fork it over, a fork spike deep. I did a lawn that is about 10 times the size of that with a fork, good workout.