Don't hurt your engine by trying to use AFR on E85, you need to read it in the Lamda scale for alcohol
Doesn't matter as long as you know what you're trying to accomplish.
Stoich gasoline is 14.68 Stoich Meth is 6.45 Lambda 1.0
So if you're naturally aspirated and wanted to run for example .88 lambda WOT that would be gasoline 14.68 x .88 = 12.91 or meth 6.45 x .88 = 5.67
Yes you could convert gauge output to lambda or change it to meth stoich as a base point but doesn't matter if you don't have that option.