Nola, IF healthy (which can be said for the entire Mets' pitching staff), is a top pitcher.
In his career (including the 9 starts or so when his arm was falling off last season), 36 starts, 204 IP, 3.45 FIP, 4.1 WAR (FG), 2.1 WAR (BR)
Which is right where Hamels was at the same age.
He turns 24 in June. His velocity has ticked up this year, which Nola attributes to using his legs more, it's natural for a young pitcher to add 1-2 MPH as he matures, Hamels didn't hit his peak velocity until 2014.
Now whether you want to quibble over whether he's a #1 or #2 starter, a healthy Nola will be a top starter for the next decade. A reliable 3-4 WAR pitcher.
The question, as with most young pitchers, is whether he can stay healthy.
As far as Hellickson, you take what you can get for him, then see among Thompson, Eshelman, Lively and Pivetta, who's the most ML ready and bring them up.
It's a rebuilding year, we want to continue to add prospects, and at some point you have to give the kids a taste of the big leagues, but in August, not April.
Hopefully we can move Hellickson, Benoit, Saunders and Nava, or at least 2-3 of them.