Almost certainly yes. That is the entire reason to stay on 1.5.97. Mods that never updated for AE will work flawlessly with USSEP 4.2.5.
You must first downgrade using the Unofficial Skyrim Special Edition Downgrade Patcher (available on Nexus). This tool reverts your 1.6.x executable and master files to 1.5.97. Then install USSEP 4.2.5. Unofficial Skyrim Special Edition Patch 1.5 97 Download
Yes, simply use the latest USSEP from Nexus Mods. The 1.5.97 version is specifically for downgraded setups. Almost certainly yes