in some cases like Flail mowers, manufactures will state a certain HP to get a bigger(heavier) tractor. It does not take the HP to run it, but the bigger tractor to handle the weight. My Bobcat CT 235 is a heavy tractor for its hp - 3600 lbs vers 2800 for a different brand. The YJR 074 is supposed to need 50 hp (now down to 40) the big reason for this is it is heavy. My YJR weighs close to 1000 lbs, but I see its on a diet now at 919lbs but they did change the 3pt frame. I know it is back there, and it can lug my tractor down, but I just slow up and let things recover. With a gear drive tractor that can be a problem. So the manufacturers weigh on the side of caution.
I was told I could not run a full size baler with my tractor and that I had to go mini. Got to thinking about the old days and what farmers used back then, Tractors were heavier but about the same power. Bottom line - I run a full size Hesston 4550 baler without problem, even sub 450 rpm. I am just not fast but I get it done. One thing I do is test operate each unit before I buy - the exception is the new flail mower I have coming. However I did go lift a piece of equipment with the same weight and dimensions to check.
So HP requirements are relatively close and there so everyone is happy - can you run with less HP - probably, but not as fast as a bigger tractor would do. Given the size of you unit, try out some tillers first - even some of the lighter models are good such as from TCS and others - you can add weight to stabilize and many folks love them. Do a search You can trade up later. If you let us know where in California you are, others may be able to help better. There has got to be a rental place or Agg dealer somewhere near you. Check Craigslist too.
at this procedure). Each year it is getting better. It used to take 4 passes to loosen up, now only 2 with the second pass cross the first at full 8" debth. With my tiller I have the rear gate set tight against the springs, so it compresses after tilling, making things ready to plant.