Hi Landon, welcome to MP3car.com. The easiest system would be a stalk mounted small laptop, with a bluetooth audio receiver connected to you amp inpur or aux input of existing car stereo.
The next level up would be a trunk mounted carpc, with either a dash or stalk mounted screen depending upon size required.
The most aggressive would be a double din pc.
With and windows or mac based carpc you can plug in a usb monitor, where video and power come from the single usb plug. Up to 15" in size it would be easier to see photos on while parked somewhere.
Price can be any thing from $200-$500 for used to $500+ for a new system depending on requirements.
Android based systems might not be good due to compatibility with external hard drives.