I like the trade ideas, individually, but you're right that this team needs to sign Gusev and Karlsson, and then hope for good chemistry to contend any time soon. Signing those two is much easier with Ovechkin and Backstrom than without them. Cap moves can be made at a loss afterwards, if necessary, since both will be UFAs next summer.
Of course, if Galiev is still an RFA, his .79 playoff ppg this Spring were about as good as Gusev's .80 (
https://en.khl.ru/stat/leaders/472/pts/). I have no idea whether Reirden left a better impression on Galiev than Trotz did, but it's worth noting that for all of the year and a half Galiev spent on the Caps roster, he got four points in just 209 minutes of icetime. That's how much John Carlson play in eight games, but it took him 26. Definitely better to leave him in Ak Bars this year where he plays top line and develops, and then consider signing him next summer if/when one of DSP/Connolly walks. Gusev has had three years of ppg regular seasons in Russia. Galiev, at the same age, has done his best work in the AHL, and on the Caps' practice squad. He definitely needs to stay where he can get icetime, but I don't see either of them signing up to join the Caps right after Ovechkin leaves. I could definitely see both of them signing up to play next summer if Connolly and DSP are too expensive and the Caps convince Ovechkin to call them up and ask nicely.
Karlsson wants to win. He wants to be a big star. Joining a medium market team like the Caps would be a push except that they just won the Cup and they have arguably the best group of Swedish players in the NHL (for now. Buffalo will hold the honor in two years, whether or not it signs EK). Keeping Backstrom, Burakovsky, Djoos, and AJF in the fold gives Washington pretty good odds to convince Karlsson that, for the same money, he'll have a better time playing in DC.