Right ideas for Sabres: targeting Karlsson for the 2C need, Trouba for Dahlin's partner and shedding Scandella, Larsson and Girgensons.

There are several flaws in your approach though:
1. Vegas would only trade Karlssson because they're over the cap now before he even gets re-signed at his current salary, much less the raise he'll be seeking. They can't afford to take Ristolainen's cap hit.
2. Same issue with the Lightning - even if the Sabres retain $1.5M as you propose, they won't want to add $2.5M on top of their current cap when all of the signs are they will need to dump salaries this summer in order to afford re-signing Point.
3. Skinner won't sign for under $8M in Buffalo because of the simple math: any other team can only offer 7 years and no one would pay him more than $9.5M (what Stone got), meaning the best deal he could get outside of Buffalo would be $66.5M. In order to top that with the 8th year of term only Buffalo can offer, they would need to pay him at least $8.3M. That's why most Sabre fans who want to see him stay are expecting a deal in the $8.5M - 9M range.
4. The salaries and remaining term for Neal and Okposo make a swap reasonable to consider - but since both players are slow skaters with diminishing skills, what needs to be considered is the locker room element. Okposo wore an 'A' last year and is very well-liked and respected as a leader off the ice. Neal has a reputation with some of his past teams of being difficult with teammates and coaches. With all of the focus management has put on 'culture', it seems unlikely they'd make the trade IMO.

All solid points. My response to those:

1. Thought process for Vegas was they badly need RHD and a Risto for Karlsson swap saves them at least $1.5 million on the cap for 3 years (pretty good for high caliber players)
2. With all the vets TB is losing on the back end (Coburn, Straalman, Girardi, Ruuta are all UFA's) the thinking here was just for Tampa to get a top 6 veteran D at a relatively low cost with no future commitment. If it works out, resigning will be a piece of cake. A 6th round pick is nothing to TB... a win-win for both so BUF can go younger (Pilut).
3. Skinner and Stone are not good comparables IMO. Stone is much stronger in the defensive end and is a point-per-game player (Skinner is not). Sure, Skinner may be a better goal scorer, but the $9.5 million cap hit is attested to a better all around player
4. Bad teams need to make changes, that simple. Neal wasn't a fit in Calgary and Okposo hasn't panned out in Buffalo. Cutting ties for players at the same age with the same contract status is worth it IMO. Who knows, Neal could fit in great for Buffalo (sorta like Niederitter did for Carolina vs. his poor production in Minny). Could also potentially say the same for Okposo. That is my thought process.