Not renting a car but taking the ME from the airport to a DW resort and staying overnight sounds like a great idea! The ME can take you to port do that's a fabulous option! No park visits but we can hang out and eat at the resorts. No character meals. My son doesn't like them unless they have normal sized heads and bodies. Thank you for this idea!
Well, if your son does not like the characters, then skip the Chef Mickeys idea. Still, taking a trip on the Monorail would be a lot of fun for both of you. You would get to see some of Epcot and a little bit of Magic Kingdom.
As far as taking a Disney bus to the port, I am not 100% sure if you can do that unless you booked a Disney land and sea package. If you are not taking a
Disney cruise at all, taking the Disney bus to the port won't happen at all. However, if you booked a Disney cruise, you might have to call and ask if you can take the Disney bus to the port from your hotel. I don't see why it would be a problem, but calling them and letting them know is a good idea so they know how many people are at the hotel to pick up. If all else fails, you can take a shuttle bus or a taxi to the port.
However, taking the ME bus from the airport to your hotel is something that you can for sure do and will save you a little money!
I think doing something like this, were you arrive in the evening, maybe take the Disney buses to Epcot or MK to ride the Monorail or take the buses to DTD will give you a great feel for how their transportation systems work and will allow you to see how your son will deal with them. Also, whenever you do decide to visit WDW, you will already know how to get around, which can be a headache for some people.
If you are looking for a cheap Disney hotel, I reall suggest Pop Century or the brand new Art of Animation. However, Art of Animation (while still a value hotel) will not be totally open yet I don't think so they might only have family suites open for booking which cost a lot. Pop has a great place to eat at the hotel with a really nice counter service breakfast, some nice (but simple) pools, and an arcade.
One fun thing to do however if you do stay at Pop would be to cross the bridge to Art of Animation (they are like right next to each other) and look around. From the concept art I have looked at and some of the constuction pictures I have seen, it looks like a really nice value hotel with lots of fun things your son will enjoy looking at!