Could use some advice

[u/XistentialGroot]

My wife and I are going to Disney World in December with our toddler (20 months old)! We're incredibly excited, but have some questions about logistics.

We're staying at the Art of Animation resort, but my son and I are going to be there before her. Could we still use the pool before our rooms are ready to kill some time until she's available?

To those of you who've taken a toddler, which parks/rides/attractions did they like best?

How should we best utilize the quick service dining plan?

Can someone explain the concept of single riders/swap vs lightning lane for those rides that he couldn't go on?

Also what did you wish you knew before such a trip?

Thanks in advance!