I apologize, I don't think I made my point very clearly. My response was too cursory to address the complexity in your original post or to provide full context of what I was thinking. I also did not intend to make it sound like you wanted to skip steps.
First, let me say, that among Sharks' prospects, not including Smith and Celebrini, the only ones that I think have a realistic shot to make the team out of camp are Gushchin, Graf and Musty. Gushchin because he has the most offensive ability among those 3, Graf because he has the best 2 way game, and Musty only if the Sharks don't see enough value you in sending him back to the OHL and he proves that he can hold his own in the preseason. I could see him getting 9 games and practicing and training with the Sharks for a few months before a final decision is made. I didn't include Bordeleau in that list because I don't think he's better than Gushchin offensively or Graf defensively. However, that doesn't mean he won't have a chance, as all 3 are waiver exempt to start the season. Bystedt, Edstrom, and any other guys aren't in consideration.
So, in terms of the top 6 next year, I'm perfectly comfortable going in with something like the following (line combos are essentially random):
Eklund-Celebrini-Zetterlund
Smith-Granlund-Couture/Graf/Musty/Gushchin
Hypothetical bottom 6:
Kostin-Couture/UFA-Graf/Kunin
Smith-Sturm-UFA
Obviously, if Couture is healthy that makes the decision easier, because then you don't really need a prospect, besides Smith or Celebrini, to step into a significant top 6 role. If none of Graf, Musty or Gushchin or whoever is ready for that, you still have Kostin or Kunin or whoever else the coach feels more comfortable throwing up there. If Couture is not healthy, then I think it would required to sign a 3C.
Regarding your lineup, where you placed Couture on the 3rd line with Smith, that's totally acceptable too. However, I would assume that's less likely if Couture can even play. If Couture is relegated to the 3rd line, then I would assume you had to acquire players like Dakota Joshua or Anders Lee to force him down. It's not a difficult leap to get on board with the idea of adding one mid-level UFA like Joshua. Also, if taking on Anders Lee includes a draft pick in the 1st 2 rounds, then great.
Hopefully this clears up the idea that I'm advocating for "stuffing the lineup full of children."
Regarding my comments on the defense, you didn't address those, so I'll just assume you're cool with that part.