Hi, and Good Camping, We've got a 282 RK Hemishpere and love it. Anyway, if the previous owner is up to it, have them go over the basic details, such as where is the water pump and heater, bypass valve, fuses/breakers, etc. There are some good posts on pdi's (pre delivery inspections) which can help point out what you need to know, or questions to ask.
Driveway camp the first night or two and make sure everything works and you know how to work it. That goes for stuff you may not need at this time of the year such as furnace, but make sure it works. Have the previous owner set it up and show you how every appliance operates.
As for what you need, the basics are wheel chocks, leveling blocks, stabilizing pads, white potable water hose, sewer hook up hoses, RV toilet paper and chemicals, electric cord and adaptors.
Mark, Vicki, & Scout THE dog
2015 Hemisphere 282RK
2010 F250 Super Duty
1992 Goldwing Aspencade