Letting Welker go tells me that the Patriots want to focus their offense completely around Gronkowski and Hernandez. The WR and RB will be complementary elements to the attack. 2010 and most of 2011 proved that when both are healthy together, it is a devastating duo.
So you figure, Gronkowski and Hernandez would be the de-facto Number 1 and 2 targets, respectively.
At WR, the Patriots have signed Amendola and have reportedly agreed to terms with Donald Jones.
I see Amendola as a more traditional Z receiver and not a true Welker replacement. In regard to Depth, I think Amendola will turn out to be the Number 2 WR. Donald Jones is solid, but if he is starting there are serious issues at hand. He could be a Number 3 or 4 option. So too could Edelman if he is resigned.
For a Number 1 Receiver, the Patriots need to draft a big, strong, speedy player in the draft, or sign someone who has those traits (DHB is a classic example. A home run hitter). If Brandon Lloyd is retained, I'd expect him to fill this role.
My vision for WR depth would be as follows then:
1 - Brandon Lloyd <Or Draft Pick/FA, preferably)
2 - Danny Amendola
3 - Donald Jones (Backup X receiver)
4 - Julian Edelman (Backup Z receiver)
5 - Matthew Slater
There is also room for an additional WR if needed. I just think that in retrospect, if the offense is going to be run through the Tight Ends, and they stay healthy, the Patriots don't need big time WR.