Let's assume that Ryan McDonough is serious when he says that it is NOT desirable to have multiple young guys at the same position. That he really believes it would stunt the growth of one/both of those young players.
That would mean that we should have a veteran at each position. Preferably, a veteran who makes a good role model for that younger player. Let's put that in a table:
Our need for a Shooting Guard or Center is pretty well documented here at BSotS, and we can readily see that we can afford to plug a young player in either of those spots. Another possibility is drafting a PG with the size to play some SG (e.g. Michael Carter-Williams or Nate Wolters) and playing lineups with 2 oversized PG's.
There has been a lot of talk about trading Gortat, due to his expiring contract. However, we don't have a veteran replacement ready at this point to fill that hole. Should we trade him, that is a need we will have to address. Because we don't have a prospect type of player at that position who can step in and assume minutes there, the problem is doubly concerning. If we trade Gortat, we either must get back a veteran center, or else go sign one in free agency. Maybe you can plug Channing Frye into that role, but I would be very concerned about counting on a guy who just missed a whole season to come back and provide any level of production.
A need that I haven't heard much about at all is the lack of a veteran small forward. (No, PJ Tucker isn't a SF.) That's something the front office should address. A potential candidate would be Mike Dunleavy Jr, who fits the bill as a high-IQ veteran who wouldn't break the bank and could mentor a younger player. He also fits a need as a shooter, as none of our SF's this past season were reliable enough threats beyond the arc to create space for the offense to operate.
Looking at the chart, the positions where we can best afford to trade someone are the SG or PF positions, where we have multiple veterans. Tucker and Frye likely aren't worth much in trade, so that means Scola and/or Dudley.
Because Channing's early season conditioning is a major question mark, because Scola can't be moved on draft day, and because we have no immediate center to replace Marcin Gortat, a mid-season trade of Scola and/or Gortat makes the most sense. Preferably you get back a prospect at whichever position you didn't fill with the #5 pick this year. With the new salary caps, there will be contending teams looking to trade out, even in a "deep" draft.
Finally, Markieff Morris has proven to me that he isn't an NBA player. Strangely, I don't feel the same way about his brother, as his ability to stretch the floor with his range is an NBA skill that almost always translates into being at least a spot backup (12-14 minute guy). If the Suns brass feel the same, it would make some sense to bring in a prospect type player at PF, as well (e.g. Bennett).