I used to use https://liquesce.codeplex.com/ which I believe was based on Dokan prior to being silently abandoned by the developer.

Is Dokan the appropriate library to build a disk pooling solution on top of? If so, can you recommend any such projects?

TLDR - Create a "Dokan" folder on each of my 5 physical drives, present a drive to my OS that shows all files from these 5 drives as if they were one physical drive.

Yes Dokan is able to do what you describe. There is a mirror example in the repository that mirror a device or folder. With a little of changes based to the mirror, you can create a sub directory for each of your devices in on folder. (Create a fake main directory that list all directories of your device and after reroute all file opening request to the right device)