[How-To-Updated 2021] Installing AdGuardHome on OpenWrt [Manual and opkg method]

What are the storage space requirements when installing AdGuardHome via LuCi from the Software page (opkg)?

I installed AdGuard on my Linksys E8450 / Belkin RT3200. Do I need to worry about running out of storage space (when I upgrade in the future)? The wiki mentions the agh-backup folder and a 100MB free disk/flash space requirement. Does this apply when installing via opkg? Also seems like the filter lists are stored in RAM.

Similar question was asked on Reddit. Perhaps we can update the wiki regarding storage space requirements.