While getting a top cog like Burns or Bishop could be beneficial for LV, they may be better off just tanking for the first 2-3 seasons and getting high picks. Giving the ice time to younger players they will get in the expansion draft would be good for their development too. Sure, McPhee will have a lot of cap space, but building a team through free agency does not equal success.
The novelty of having a hockey team in Las Vegas will carry the team at the gates early on even if they suck. People visiting from all over North America will go see the arena and watch their own favorite team play. The rink will likely be full on most nights.
Then, once their top-5 picks start getting NHL experience and making noise, Las Vegas will still have enough cap space to make trades or sign players to fill holes and become a playoff contender. That's how they should build the team. 4 or 5 years in they could be a top team in the league, depending on the quality of prospects they draft. The more they suck, the more chances they have at landing the #1 pick.