This has been interesting. And this info might be a little off topic, but I think it's still in the ballpark. I was at a local MF/MAH dealer looking at tractors about six weeks ago. The sales man told me that CUT's don't have enough hydraulic power to run a backhoe. Which caused me pause. He actually told me that backhoe's on CUT's are PTO powered with their own hydraulic systems.
However, when I was at the LS dealer (different dealer just so you know) the business owner told me that LS tractors have more than enough hydraulic power to run a backhoe. I have known the LS business dealer for many years and he's a pretty straight shooter. In fact he used to be a MAH dealer before switching over. Now he also sells Bransons too. Maybe LS is using smaller hydraulic cylinders on their backhoes?
But anyway, I just thought I would put that out. I can see both sides of the issue. If you have a failure in one system it won't contaminate the other system if the backhoe is PTO driven. But if your tractor has an adequate hydraulic system why not use it for the backhoe and save money/resources re-inventing the wheel. Just make sure you have an adequate filtering system. B.
The two parameters of hydraulic "power" are pressure and flow rate.
Not directly related, but you can think of pressure as affecting force and flow as affecting speed.
Professional hoe operators want/need lots of both for productivity reasons - and they have the skills to use all they can get.
Many/most casual users (such as myself) with occasional projects that don't have to be done very quickly can get by very well on just adequate pressure, i.e. we aren't too worried about saving fractions of seconds with every swing of the boom (-:
My 8 1/2 ft Amerequip hoe (re-badged) on my little 42 HP Kukje tractor runs fast enough for what I do with the engine not much above a fast idle, rarely above 1500 RPM.
For full on heavy hoe work a separate PTO driven pump and tank may be justified, for me and most other casual users it is not.
It is something that could be added later if you discover that your particular tractor's hydraulics overheat under your particular conditions doing your particular projects.
BTW Amerequip is one of the OEM manufacturers that you could finish up with if you buy tractor manufacturer x, y, or z's color coordinated back-hoe.
About all you get is the color match and a sub frame modified to fit the particular tractor's underguts, i.e. the holes for attachment pins will be in the right places.
I wouldn't worry about hydraulic fluid cross contamination, the hoe is just a few more hydraulic cylinders.