IMHO I will always have a car when at WDW, if for no other reason than to have the ability to arrive and leave a park when I choose to do so. If you have strollers it is much easier to manage I think with your own transport than having to fold a stroller up to get on the bus, find a place to stow it, then expand it again, and then do that all over again when you have to come back.
I found it very easy to drive around the WDW property. Signs are pretty much everywhere directing you to the appropriate destination. I was able to manage fairly well my first time down.
On the other hand staying at OKW you're probably not going to be prone to the hassle that other resorts face with bus service, particularly those around Epcot. Still, I'd rather make my own schedule.
The one earlier poster who made mention that it took them over 2 hours to get back to their room after the Halloween party is correct. On nights when there's a special event such as this you should expect a rather lengthy delay getting out, especially if you're leaving with everyone else. Two years ago we left MK right after Wishes, and it started to rain, so guess what? Everyone else decided to leave. We had our car valeted at CR as we had eaten at Chef Mickey's that night and decided to monorail over for the fireworks and Spectromagic. Well...it took us about 45 minutes to get a monorail and get to the CR to pick up our car. Once we had our car getting out wasn't a problem. The point to this story, leave before everyone else, or let it thin out a bit and take your time getting out.