What is the shelf life? Can I take a month or so to finish a barrel?
This depends on storage conditions and your care to keep caps tight etc.
My barrels of fuel lasted me a whole year +
Also invest in a e85 tester ..... My e85 never fell below 80 Not all E85 is E85... It can and sometimes is pumped slightly lower..
Remember ..... That E85 tank at the station is not refreshed as much as regular octane. Not many people use E85 in the New England states compared to mid western states. Point made here is that it maintains a long time..
I was running well over 800 RWHP and being at that HP level you need good fuel. Don't stress out on octane ratings as much with E85. It does not detonate like race fuel or regular pump gas...
As an example... I'd fill two 55 gallon drums up let's say in late summer (I never bought winter E85) and it would sit in my garage where I was pulling from each barrel for more than a year! (I didn't drive my car much) so fuel sat long times.
Winter E85 is been said not to be as good as Mid spring to late summer E85.
One last thing.... I left E85 in my fuel tank in my car, never drained it and it had NO adverse effects so there is no need to drain the fuel out during laid up months.