This is a great project) I see the advantage of milling the undercarrige from one piece, as one save quite much hours compared to build it the traditional way with plates. Gets a bit more heavy to carry around, but the machine will sit more stable, so I guess it is mostly an advantage. Eletric motors for the tracks are quite more efficient than hydraulic ones, but I guess you like to experiment to see if it is possible to make hydraulic motors work on a model excavator) From an technical point of view, it is more interesting and challanging to install hydraulic motors, I agree to that
Look forward to see the finished machine, keep on the good work)