Will I be able to create a Bootcamp partition that I can boot into from Parallels once I've upgraded to High Sierra?
Yes, but there are a few issues. See Known issues with macOS 10.13 High Sierra and Parallels Desktop for Mac:
- Cannot create a new Boot Camp VM. Fixed in version 13.1.0
- Cannot start an existing Boot Camp VM. Fixed in version 13.1.0
- Cannot install macOS High Sierra to a virtual machine with Apple File System type. Fixed in version 13.1.0
- Cannot install Kaspersky Internet Security for Mac on macOS 10.13 High Sierra. No workaround.
- Video artefacts when switching desktop spaces in Full Screen mode. No workaround.
- A VM installed from Mac Recovery partition cannot upgrade to macOS High Sierra. No workaround.
- Parallels Tools system extensions are blocked in macOS High Sierra VM. In macOS High Sierra VM open System Preferences > Security & Privacy > General > click 'Allow'. See KB 124244
- Cannot deploy Parallels Desktop to Macs with macOS High Sierra (host OS). See KB 124289