Pettersson at $2 million, ZAR at $900k and Riikola at $750k gives you:
Guentzel-Crosby-Rust
Simon-Malkin-Hornqvist
Pearson-XXXXX-Kessel
ZAR-XXXXX-XXXXX
XXXXX-XXXXX
Dumoulin-Letang
Maatta-Schultz
Pettersson-Johnson
Riikola
Murray-DeSmith
That lineup costs $77.15 million, and even assuming you go super cheap with the other 4 forward spots (let's assume you get WBS guys or veterans all at league minimum), you're at about $79.75 with your 3C spot left to fill. Realistically, it's likely going to be a little higher than that, because Blueger, Dea and Blandisi (all guys I expect to be depth players for next year) have qualifying offers over league minimum.
If the cap doesn't sizably increase, you're basically stuck with finding another 2017 Sheahan. You're at $80 million already even with moving Oleksiak and not bringing any cap back.
Oh yeah I'd be happy about that too, but I said "best case" for a reason. You'd have to be incredibly lucky to pull that off, that's like striking gold with getting someone like Faksa or Jarnkrok. Personally, I'd be calling Nashville right now and offering anything they wanted for Jarnkrok. Getting a 3C who's signed for like 3 years at $2.1 million would be insanely good, I'd be willing to offer a ton for him.