DET looks dangerous, but their D is just... eh. The bottom 4 could be OK, but with all this money on the table, why not take a swing? I feel that Dumba could bring some extra stability here, especially if he keeps up the physicality game he brought vs DAL in the playoffs. It could compliment GhostBear's offense well.
Swap Maatta and Holl as needed. Swap the whole middle 6 forwards as needed as well, but that's how I'd draw it up.
The only thing I know about Veleno is that bonehead play he made in the IIHF this year. With an extra 3mil on the table make his contract whatever if needed.
Signing Dumba to a multi-year deal at 5M is going to require letting every ufa go, just to re-sign Seider and Raymond probably. Then there are 3 more RFAs + the ufa replacements. With the way, things currently are, all it should take is shipping off Fabbri (at 50%)+ Perron off the books to lock both Seider and Raymond (probably have extra). Then they can spend that 5M to re-sign Ghost if he's a good fit or for a top 6 player if that's what is needed more.
Best to go with what they have now, and see what actually needs to be improved through the season.