Very nice. I would not have thought of moving Okposo to make space to sign Duchene,
We all have a different evaluation of the Sabre talent so yours may be better than mine, but here is my pea brain evaluation.
Larsson and Girgensons are nearly equal. Girgensons is a little more physical, Larsson is a better center, I think their trade value would be about the same.
I think Scandella has some value, but your concept is fair and maybe what it takes to move his $4,000,000 contract.
This site was developed by examining the trades GM's made to exchange draft picks
https://www.broadstreethockey.com/2013/4/25/4262594/nhl-draft-pick-value-trading-up Buffalo's 2 first round picks is a bit of an over payment based on this data. Asplund, Rasmus and Thompson, Tage could be taken out of the trade. As a matter of fact, using that site to make the trade fair Colorado would need to add Ottawa's 3rd round pick.
IMO Tampa would love that trade.
While i think Okposo has value if used properly, giving up a first round draft pick to make room for Duchene seems to make sense.
Over all very plausible as I think Buffalo is over paying in nearly every trade, but as I said, I may be overvaluing the Sabre assets.