Buffalo says no if they have to retain that much would need to add another B+ prospect and atleast a 2nd rounder for them to think about it but more then likley would ask for another 1st

Flame don't do that Buffalo trade. Make it Zary Monahan Dube 2022 1st for Eichel no retention and don't do the Arizona deal and have Lindholm take 2c
Line up will look like this with Eichel from trade above IMO
Gaudreau Eichel Tkachuk
Mangiapane Lindholm Coleman
Lucic Backlund Lewis/Pitlick/Ritchie
Ritchie/Lewis/Pitlick Gawdin/Ruzicka again Gawdin/Ruzicka

i cant see any team holding 2.6m$ for 5 years after trading a player, maybe 1m$ as a max. could bite hard down the line
tho i dont see why buffalo wouldn't withhold salary on both players heading over if its a cap issue for just this 1 year hit mainly.
so miller 1.6m$ retained for 1 year and Eichel for 1m$ for 5 years.

I like both of your options.
I sort of preferred Zary at one time but now I think I like Coronato more.
Välimäki, and 2022 2nd is not sufficient for the retention on Jack, Miller and the third.
Especially considering Välimäki is a LHD, Buffalo's deepest and strongest position.