Hi Michael!
I brought my son to Disney in 2008 at 18 months, so I definitely empathize on the "entertain" question.
What our family did was split up. My wife would wait in line with my daughter, who was older and could get on the bigger rides, while I would take my son and go over to toddler friendly rides, or places that a 18 month old couldn't get in trouble (smile). For example, while at Epcot, my wife and daughter went on Soarin while I walked over to Innoventions with my son, which he loved!
My son also loved a Buzz Lightyear spin toy, which the theme parks sell for a variety of Disney characters. You press a button and it spins with all these colors. I had to pull that out a few times when we stayed in line.
But kids at that age can be unpredictable (example: the Buzz Lightyear toy didn't entertain him by the 3rd ride-smile), so do the best you can.
For strollers: it was worth it paying the extra money and renting a stroller at the theme parks. When our daughter was a toddler, we brought our own stroller, but lugging it around from resort-to bus-to theme park, then all over again leaving the park, got frustrating. If you do decide to bring a stroller, get one of those inexpensive small ones from a department store before you come. One that will get you in and out of traffic easy at the parks, and folds up quick. The baby carrier may work, but at 18 months, my son didn't last 3 minutes (smile).
Good luck and hope you have an exciting, stress-free trip!