Peters and Gunter (DT/DE)
I see no issue with these two rotating at NT.
One would hope Olson Pierre can regain his effectiveness at DE, as well.
On paper I would put the following out as your starting 3-4 DL.
Gunter
Peters
Pierre
with the backups (as it stands now)
Nkimdiche
Valentine
________
The Cardinals still have Vincent Valentine, not sure if he is NFL talent, but he could play NT, and believe he did so for the Patriots earlier on in his career.
I would not hurt for the Cardinals to pick up a DE, but it is not critical, IMHO. Robert Nkimdiche is strictly a backup/situational/depth player at this point.
That all being said, the Cardinals still have to re-sign Rodney Gunter who is currently.
That all being said, there are some solid depth DE's out there, and Robert Nkimdiche seemed like he played better in a 4-3 (maybe use him for trade bait in the draft?). So, I would not be surprised if they signed one of the following in free agency.
Henry Anderson
Damion Square
Brent Urban
Grady Jarrett
Darius Philon
Christian Covington
Zach Kerr (Played for the Broncos last year, could play NT, has the body for it)