Regarding the geometry of the three point hitch (item 2) I forgot to mention one important aspect. The lower lift arms, if viewed from above, should NOT be parallel. The distance between the attachment points of the lower lift arms to the plow should be larger than the distance between the attachment points to the tractor frame.
For ground engaging implements, especially plows, this is critical for proper tracking.
I have seen some aftermarket 3-point hitches where the lift arms are parallel. These are fine for lifting but not for pulling ground engaging implements.