there was some discussion about devicepages in the LEDE wiki, but we havn't yet come to "the" conclusion regarding a template.
If you don't have a better place to put them, just use /toh/<brand>/<model>
I know from the OpenWrt wiki that you know what you are doing, therefore: Go ahead, freestyle, create examples / templates that others can follow.
When adding devicepages for devices that are already present in the ToH, consider using datatables to include the ToH info into the devicepages.
In case of questions, just let me know.
P.S.: There are two ways to ease creation of devicepages in the LEDE wiki