Belated welcome to the forum,
DeliveryGuy89!
I did an eco-driving session with an AWD Subie owner (about the same vintage of yours, but automatic), and was surprised how thirsty it was (not knowing the EPA numbers ahead of time).
Sounds like you're a big fan of the brand, but I'd be planning ahead: are there any better MPG options in your price range with AWD? You cut your fuel consumption in half during the non-snow months with an additional vehicle - is that an option?
Until then, follow the good advice given so far. I suspect you won't find a
huge improvement in your numbers considering how much effort you're already putting in. PS: kudos for doing delivery with a manual. That helps a TON if you're driving it well.
PPS: Nokian makes a really LRR winter tire, from what I've read. Lemme see if I can find it...
Edit - here's one thread:
Riding on Nokian LRR winter tires: R2