Since you don't have a ridge beam, without the tension tie, there is nothing keeping the dead load of the roof from pushing down and pushing the walls out. Full length top plate won't stop that. Lower snow load helps for sure.
That being said, it's a small shed with a small span and any issues...
This makes no sense to me. Is your basement 'conditioned' space? My guess is that yes, your basement is conditioned space. It makes no sense to exhaust to exterior, and intake fresh air from the conditioned space.
Advanced framing is about maximizing energy efficiency, not just minimizing cost. By minimizing wood members, you are creating a structure that will perform better from an energy perspective. It will have more cavity space for insulation, less thermal transfer, etc.
I love the blue siding. If my neighbours didn't go with blue, we would be when we renovate our place.
Hopefully you can make some good progress this week despite the snow. Everybody is freaking out here about upcoming snowpocalypse (which will end up being a few flurries).