Ultimately only you can answer that question, but there are factors you need to consider in making your decision, especially as your requirements seem to be a bit heavier duty than the average home-brewer.
1) Ergonomics, which in turn affects the size of the hopperS. It's no use having a feed hopper than can hold 25kg of malt if the container catching the milled malt can only hold 5kg. So you need to work out what size hoppers you can fit and still be able to easily load it. A feed hopper that's too high will be bloody awkward to load, especially from a bag. Depending on your brewing setup it may be difficult to lift large amounts of milled grain to tip into the mash tun, so consider also the size of the receiving hopper.
2) Obviously you want to motorise the mill in such a way that you don't have to stand there holding a drill, but how quickly do you need to process 25kg of grain? Is there really a need for speed? Or would it be OK to mill a bit slower, since you should be able load it up and walk away until the grain is cracked (even if you have to load the hopper twice, as per the previous point). Duty cycle will also have to be considered. No good having a mill that can only work for 10 minutes at a time, if it will take 20 minutes to mill all the grain you need.
3) Cost. If (like most of us) you're on a budget, you may have to sacrifice certain features to afford those you really need. Some of these options you may be able to add later. But you may have to make provision for these later additions in your initial planning to avoid additional cost or inconvenience/frustration when that later date comes.
4) There's more to setting up a mill than just buying a mill, motor, and the bits to couple them together. Motor speed versus mill speed -- will you need a reduction system? Will the mill be fixed in place (like on a workbench)? On a stand you have to carry around? How much will all this weigh, and how awkward will it be to carry? Maybe you could put wheels on the frame? And where will you store it?
I'm sure there's other things to consider, but I can't think of them right now.