I like the cap breakdown, but I don't think either of those trade proposals are very realistic. Ottawa should be able to get way more than that for Hoffman. That package is bottom pairing D man who is slightly overpaid, a 24 year old D prospect with 13 career NHL games played, a 24 year old long shot goalie prospect with 13 minutes NHL experience and a 2nd round pick. There is no 'really good'asset in that package. I'm not even sure that there is simply a 'good' asset in that package. Schmaltz was hurt by a log jam ahead of him at RD, but this year he couldn't beat out Bort for a 3rd pairing spot and got surpassed by Dunn. That's no longer a top level asset.
To make your hypothetical work, I think we would need to give up Fabbri or one of the top 4 prospects (and that might not do it if Ottawa isn't eager to take on Gunnar's contract). Hoffman only has a 10 team no trade list, so there should still be a number of bidders on a defensively sound, 55-60 point guy who is 28 with 2 more years on a reasonable contract. An average/slightly below average roster player and collection of expendable assets shouldn't be close to what they can get for him. If that's all they can get, they would likely just keep him for a year or two and trade him as a rental for more than that.
I also don't think Sobotka returns nearly that much, but the return for Sobotka isn't all that important if you can find a way to add Tavares and Hoffman to the roster without crippling the future.