Firewall, ask what you want. (What hardware, software is implemented, how is it monitored and service levels maintained.)
VPN (site to site). What type of hardware (VPN server), clients are recommended? What QoS and reliability, data rate guarantees (if with ISP), how changes and additions can be made, billed.
Like already mentioned, what types of protocols will you use (encapsulate) over the PPTP/L2TP VPN, what levels of encryption are recommended and what is the full effect of different levels of encryption on actual data throughput? (You will be surprised at how much bandwidth is used by encryption as it becomers more secure, with greater bit depth. I also assume IP is used as the VPN transport, otherwise there will be no way to ecrypt and transport your protocol across the internet.) Of course, if your business has point-to-point circuits (usually leased lines), then you can use ANY protocol your business prefers.
Hope this helps