As the Seahawks quickly get ready to embark on the second half of their season, their roster — like many around the NFL — looks quite a bit different than it did when the season started.

Seattle will head to Arizona without starters Cliff Avril, Chris Carson and Luke Joeckel. But John Schneider also has added Duane Brown and Dwight Freeney, who already have made their presences felt and will be big parts of the second-half playoff push.

As he tries to help the Hawks become a contender this season, Schneider also is evaluating and plotting his 2018 moves.

Schneider’s blockbuster trades for Sheldon Richardson (on the eve of the season) and Brown (at the deadline) have been perceived as the Seahawks selling out for this season, because the Hawks gave up next year’s second and third picks and their 2019 second-rounder in those two deals. They were indeed bold moves to fortify positions of weakness after Malik McDowell and George Fant were injured during the summer, but they will pay off beyond this year — one way or another.

Brown is signed for another year, and Schneider indicated he wants to re-sign him beyond that. Both said they want the 32-year-old Brown to retire a Seahawk. So add him to the 2018 extension list that includes Earl Thomas, K.J. Wright, Frank Clark, Tyler Lockett and perhaps Richard Sherman.

Richardson, meanwhile, will be the headliner in a 2018 free-agent class that is scheduled to include Joeckel, Jimmy Graham, Paul Richardson, DeShawn Shead, Blair Walsh, Eddie Lacy and Luke Willson (among about 20).

Now that Brown is on board, the Hawks are projected to have only about $19 million in 2018 cap space, which really means about $13 million for free agents (gotta set aside money for rookie bonuses, practice squad and injury replacements). They could add $4.75 million by letting Jeremy Lane go and $7.5 million if Cliff Avril retires. That would give them a little over $25 million for 18 open roster spots.

Schneider almost surely has to make a choice between expensive “Riches” — Sheldon Richardson and Richard Sherman. Young Sheldon most likely would cost at least $13.5 million (the 2017 franchise tag for defensive tackles), leaving about $12 million for 17 roster spots.

Even if Seattle could keep him for “as little as” $10 million a year, that still would be just about $15 million for 17 guys. That’s loosely $5 million beyond minimum salaries, which means they might sign one or two non-minimum guys beyond Richardson.

If they wanted to do more than that, they would need to come up with more money. That brings us back to the much-discussed Sherman trade option. If Schneider moved the star corner, he would net Seattle another $11 million (plus at least a second-round pick, offsetting the one sent to New York for Richardson).

The Hawks could replace Sherman with Shead, paying him about the same $6 million a year they gave Lane in 2016. Then they might have up to $22 million for the remaining 17 roster spots. That would allow them to put a second-round restricted tender ($2.75 million this year) on Justin Coleman, maybe re-sign Joeckel for $5 million a year and Willson for $2 million.

Graham, Paul Richardson, Lacy and the rest likely would end up elsewhere — some of them factoring into the comp formula for 2019. Thomas Rawls (restricted) and other one-year vets could be re-signed for the minimum, with 6-8 rookies also making the 2018 team.

Of course, if Richardson’s market is more like $15 million (or more) and Schneider doesn’t want to use the tag, Richardson will go elsewhere (this seems the most likely scenario).

After the immediate free agents are dealt with, Schneider will turn to extensions for 2019 free agents. Deals for Thomas, Brown and Wright could free up enough money to extend Clark and Lockett — if the Hawks wanted to do them all. Thomas will cost $12 million or more, and Clark probably will aim for $10 million. The aging Brown probably could be kept for $10 million, Wright for $8 million, Lockett for $8 million (maybe less). If Sherman is not traded, it’s no sure thing that he will be extended either.

Here’s a look at 2018 by position:

QB: In the restructure to accommodate Brown, Russell Wilson added $2 million to his cap hit, which now sits at a team-high $23.8 million. Seattle won’t spend much for a backup — Austin Davis counts $695,000 this year.

RB: Carson will return as the lead back on a cheap rookie contract. Lacy is likely gone; the $3.56 million deal this year was pretty pointless. Rawls is not worth a tender but probably will return for one-year minimum ($705,000). Anyone else (Mike Davis, J.D. McKissic, rookie) will cost even less. And the team won’t have any more patience with C.J. Prosise’s bumps and bruises; he won’t make the team if he continues to get hurt.

WR: Richardson is making himself some money this year and seems unlikely to return. The Hawks surely would prefer to pay Lockett, whether it’s in 2018 or 2019. Amara Darboh would be expected to step up into Richardson’s spot in 2018, and the Hawks likely would draft a receiver. Doug Baldwin has an $11.9 million cap hit (fourth on the team right now) and is signed through 2020.

TE: Big decisions here with both Graham and Willson UFAs. We thought the Hawks might consider an extension for Graham, but he has had a very uneven season and there’s no way they will continue to pay him $10 million. Even $8 million is probably too much, considering they just don’t know how to use him and have bigger priorities.

OL: With Brown and Justin Britt being paid, there might not be room for the injury-addled Joeckel, even at a middling $5 million. They might just have to go with Brown, Britt and Ethan Pocic; Germain Ifedi or George Fant at right tackle; and Mark Glowinski or someone else at the other guard spot.

DL: A lot of moving parts here. Will Avril retire? Will McDowell be available? Will Richardson be too expensive? Worst case would be neither Richardson nor McDowell being an option. That would send Schneider looking for another interior pass rusher. Otherwise, the Hawks look fine here, with Mike Bennett (maybe in his last year), Clark and young tackles Jarran Reed and Nazair Jones leading the way. It’s possible Schneider will re-up Marcus Smith, Dion Jordan or even Dwight Freeney for DE depth if Avril does not return. The Hawks have done well on D-line draft picks the last three years (Clark, Reed and Jones) and probably will add another in 2018.

LB: The Wright extension is the only question here. Bobby Wagner is signed through 2019, and the Hawks will fill in the blanks as they did this year — with cheap vets.

CB: Young Shaq Griffin will be paired with either Sherman or Shead, with Coleman almost surely back as the nickel. Special-teams demon Neiko Thorpe and DeAndre Elliott will be reserve options, along with perhaps another rookie.

S: Thomas seems sure to be extended, but Bradley McDougald is likely to move on to a starting role somewhere. That would leave young Tedric Thompson in line to back up Thomas — unless the Hawks find someone better. Kam Chancellor and Delano Hill are set at strong safety (it wouldn’t be a surprise if 2018 turns out to be Chancellor’s final year).

ST: Walsh was off to a great start (12 of 13) before three costly misses vs. Washington. If he has another game like that, the Hawks will move on. If he finishes strong, they will consider a new deal. Unlike a few years ago, when the Hawks were trying hard to replace Steven Hauschka (before he became good), decent kickers can be found. Snapper Tyler Ott will be a cheap keep. Team graybeard Jon Ryan is signed through 2019 — and worth it.