I don't know if you can take DME 4 days early. If you can, can't you take it to any disney resort or is it only to the one you have booked? I've never taken it, as it seems to waste time.
You could walk from DTD to Royal Plaza - the website says 0.2 miles, and the front desk told me it's a 10 - 15 minute walk.
A cheap option is to rent a car from the airport for one day, stop for groceries if you need, or whatever, then turn it in at the location in DTD. I believe there are 3 different rental car companies with desks within walking distance to Royal Plaza - they can elaborate if you call them, or mousesavers.com has info.
From Royal Plaza to POFQ, I'd take a cab I think.
Have you looked into a transportation company for one way - about $50? Saves some time. I used *********** the last two trips, and they were great.
I could PM you a link for a good deal that includes the 4th night free plus free breakfast buffet - it was an emailing from mousesavers that isn't available on their website. I got 8 nights in an executive suite plus breakfast for $950 including tax total. Very cool! Only drawback is that you have to pay a one night nonrefundable deposit, but it was worth it to me. The cheapest was $97/night for I guess a standard room (I paid $140 for a 2 room suite) but that includes breakfast for 2 adults and at least 2 kids (I don't know if you can have as many kids as you want) plus your fourth night would be free. So $300 for 4 nights, plus tax. I love a bargain!
Good luck in your planning!