>does a proxy also tend to encrypt the data streamed between it and the end user like a VPN service would?
It could, but it's not a hard requirement. A proxy server is just like any other server, encrypting the data en route is as desired.
A VPN encrypts data as a part of securing tunnels, but it's not a hard requirement there either. As long as two computers can communicate over private IP address ranges on a WAN, it's a VPN. The Private in VPN indicates the scope of the network, not whether any data within is immediately accessible.
See also: "Private" and "Public" IP address ranges.
>does the ISP have access to the information that's being accessed via the proxy?
The ISP providing internet to the proxy server will know what the proxy server requests and receives.
>It was my understanding that proxies tending to mask where a request came from but does nothing significant with the data between it and the requester.
Correct. Again, whether the data a proxy server receives and forwards was encrypted is tangential to the task of forwarding data.
It could, but it's not a hard requirement. A proxy server is just like any other server, encrypting the data en route is as desired.
A VPN encrypts data as a part of securing tunnels, but it's not a hard requirement there either. As long as two computers can communicate over private IP address ranges on a WAN, it's a VPN. The Private in VPN indicates the scope of the network, not whether any data within is immediately accessible.
See also: "Private" and "Public" IP address ranges.
>does the ISP have access to the information that's being accessed via the proxy?
The ISP providing internet to the proxy server will know what the proxy server requests and receives.
>It was my understanding that proxies tending to mask where a request came from but does nothing significant with the data between it and the requester.
Correct. Again, whether the data a proxy server receives and forwards was encrypted is tangential to the task of forwarding data.