If I had an oven I would much prefer a dishwasher. The Fisher/Paykel drawer unit uses about 2 gallons per cycle.
I believe the OP understands he would not be able to remove the oven only as he mentions he would need to add a cooktop. It sounds like and easy change out if the dimensions work out. The OP can find all the cut off requirements on line by download the various installation manuals for the equipment he is interested in. Extending the countertop to cover the new opening would be easy and adding a drain for the new washer should not be difficult either.