Site-to-Site VPN

Hello,

Thank you for taking the time out of your day while reading this post. I need some advice about NAT and site-to-site VPN, as I am new to networking. The layout here is that I need to set a site-to-site VPN only on a few devices on my network, so these resources could become available to another company. My current CCNP book only teaches configuration if you know the other side's internal IP of resources. I'm sure this company will only want to give us their public WAN. Luckily I believe our Sonicwall 5600N will allow for IP addresses to have a NAT that I believe we can map back to our customer's public IP address. What kind of configuring would the customer have to do? Are there any foreseen issues that can arise without having knowledge of his internal private network? How can I start doing this process automatically instead of manually? Thanks in advance.