We're in almost the same boat. Kids are 8, 4, and 18mos. We've been to WDW three times since our youngest was born and have had a great experience each time. When he was 3 months, we stayed at Pop. It worked out OK but the room wasn't big enough for all of our stuff. At the time, he would sleep pretty much anywhere so the pack n play right in the middle of the room was fine. Our next trip, he was 11 months and we stayed at CBR. The bigger room worked out well and we were able to put the pack n play in the sink area and close the curtain so he couldn't see us. That allowed for naps. Also, our room was right near one of the quiet pools, so the big kids could swim while he was napping. On our most recent stay, he was 17 months and we stayed in a studio at AKV. This was definitely the biggest room and also had the sink area to put the pack n play. We actually brought a shower curtain and rod with us to block off the area again like we did at CBR.
We always come back for naps (or at least pool/downtime). I think it's critical with this age group or else everyone will be miserable in the afternoon. We also don't do parks every day. We alternate park and resort-hopping days. Helps us keep a more leisurely pace.