will installing this patch effect other mods that are already running okay?

Depends on the mod and how you choose to install the patch. If the mod ran fine using the original 3.17 DLL then it should run fine with this one installed too. Depending on the mod, you may want to ignore the Unofficial Patch python or XML files though.

If the mod provides its own custom DLL or you install the Patch as if it were a mod itself, then the Unofficial Patch will basically have no effect on the mod.

Will it work if I copy the dll file to the BAT Assets directory.
Hopefully giving me BAT 1.1 with the unofficial patch?

I seem to crash everytime with this setup right after I hit OK after founding first city.