Congratulations! So many memory making opportunities await you. We have a 2018 M32. Love our unit and remain very happy through some trials thanks to CW. The PDI Checklist from OregonCamper referenced by Danemayer is very important. Another key document is/are the Work Order(s) attached to your prospective unit. Go to the Camping World (CW) service desk with the vin of your intended unit and ask for ALL Work Order's to be printed out. Read over these carefully prior to doing your PDI. Clip boards and print outs of the PDI checklist for yourself and anyone with you will be helpful. That way you can work together by writing down items found and compare notes later. Painters tape is also helpful as you can leave a piece at each point you have a question or concern. Headlamp and/or flashlight, level, drill/screw driver with basic tips can be very helpful. Be sure they let you or "an employee who will vouch" on the roof to ensure all seams are sealed.
I recommend if you can agree on a final number, provide a deposit, but do not sign any paperwork until the PDI is completed. Also if you can wait for all repairs found in the PDI to be made prior to final paperwork. The motivation to make corrections is much greater. There will be issues found after the initial PDI, thankfully, you are purchasing a Heartland and they are AMAZING at standing behind their products.
Follow your gut and the wonderful information from your fellow Heartland owners on this forum. If it was not for all the information I learned here along with me asking Heartland about the availability of a work history document, similar to Carfax (Work Order), we would would have been stuck with a brand new 2017 M32 with an active water leak.