Now that we have a new OC in town, there are still lots of questions to be solved. The D seems simple .... they need to get a CB, LB(s), and I assume they will tag Payne. They don't need a lot on that side of the ball.
The offense is more unknown. WR and RB are pretty solid. They obviously need a better OL and TE. And the biggest question of all is what does EB see in Howell, because that likely determines what other QBs they roster. Certainly Howell will be pencilled as the started, but gotta think a vet is on their list, along with maybe another young QB.
The next 3 months should be interesting. But to me, the #1 thing is getting Howell playing time in pre-season this fall. He needs the reps if he's the QB.
I think you pretty much nailed the needs:
Def: CB, LB, tag Payne (though I'd rather just sign the guy long term now)
Offense: OL, TE, backup QB
Of all these, I put offensive line as the very top need, after which I'd prioritize Payne, then CB (on the notion that in today's NFL, CB is just so much more important than LB). But I agree with all of the needs you listed honestly.
In terms of backup QBs, the one's I've often heard mentioned: Bridgewater, Brissett, Heinicke, Minshew, Dalton all may be kind of the "level" to shoot for. Vets who won't expect to automatically start but who could push Howell and start if they needed to. And I agree with getting a vet to be #2. If we want to draft a guy, fine, but possibly bring him in as a # 3 guy unless he just knocks everyone's socks off. Who do you all like as a possible vet QB that would fit this bill? I like the idea of someone like Brissett. He's had very recent starters experience and you know he could be a steady hand in times of need. Bridgewater injury history worries me, as does Dalton's age. I love Heinicke but we've seen his limitations and I really don't want him here if half the fan base will be calling for him to start if Howell has one bad game. Minshew is intriguing; I could live with that as well...