Congrats, how exciting for you!! Also very wise with your Seneca selection
Operate EVERYTHING, especially the slides and awning. Check for slide alignment IN and OUT and any weird noises or motor struggling. Water intrusion through the picture frame gap around the slides has been a common issue and you really want an additional bead of sealant placed in those seams. Have it done professionally with blue tape marking off the edges even if your dealer won't as part of the PDI sign-off. Check that the DOT date codes on the accessible tires make sense for your year. Look for paint issues too as others have complained about the quality of post-2016 builds. If the dealer has an onsite campground, use it before driving away for good. Have fun and don't get too stressed!