since 1993, i have split my stays between disney and universal.
there is no way i could go to orlando and not hit both places.
you must do disney first. you are familiar with it and could probably do it all lin 4 days.
stay at universal on site hotels for the end of your trip. you will be spoiled after the first visit staying on site. 3 days would be good as long as it is not in the easter or spring break time period.
by staying at the on site hotels, you will have fotl priveledges. that means you use the express lines for all rides and attractions. you could spend one day each at both parks and on the third day hit some attractions/rides you want to repeat. also, spend some time at city walk.
i have taken the mears shuttle/$14 pp, cabs/ 2 pp $25 at off times, car service and car rental.
i don't like paying the fee for parking the car at universal hotels so i have stopped renting one.
i prefer the car service. i booked a 3 leg trip for this coming trip. paying $112 w/coupon for sunray and includes a free 30 minute grocery stop.
i can have 5 people in the car with no added charge. this covers mco to disney, disney to rph, rph to mco transporation.
i would think car service or taxi would work out for you.
if you go during spring break or easter break time, there will be crowds but longer hours at the park. with fotl, you will not have long waits but the park itself, resturants will be crowded. if you plan your trip at this time, book asap for UO hotels.
my first few trips to UO were for 2.5 days, it was only the studios at that time. once ioa was built, my stays for UO are 4 days. longest i have stayed on site has been 6 nights.
for a first trip, 3 nights at rph would be good.
plan on being at the park/UO when it opens
you can repeat rides you enjoyed later in the day then.
some of the attractions are not opened until later in the day.
some have set time periods/thinking horror make up show, T2, animal planet, etc......
post again if you have more questions.