We are DW fans and just tried/added Universal in January. We started and ended the trip at DW hotels (Magic Express is too great to turn down). We used Uber to get from our Disney hotel to the Cabana Bay at Universal. So easy, so cheap. Like $20 for the whole family and luggage, and only 15 minutes. I'd suggest not renting a car and just doing Uber. Two or three days at Universal is plenty, in my opinion, and then you just Uber back to your Disney hotel, stay a few days, and have DME take you to the airport.
We loved Cabana Bay. Beautiful, clean, fun, friendly, and a 20-minute walk to the park (buses took just about as long). The bowling alley and lazy river were a big hit, and the cafeteria food was fresh, healthy, and cooked to order. Plus they have Starbucks in the lobby. We didn't need Express passes since the crowds were light. At that time of year our room only cost about $120 a night.
Why only two days? To me Universal was derivative and lower quality than Disney, with the exception of the HP areas. I'm amazed that tickets cost so much, even through
Undercover Tourist. A family of four pays $600 for one day and $900 for 2-3 days, yikes! We are probably going back next year, but only for one day. I don't really want to go back at all. We had a fun trip, and it was easy and not as intense as MK, but we don't need to spend three days there. Anyway, have fun! It's worth seeing, and it's affordable if you Uber and stay at Cabana.