Michael Bennett’s new deal is the first of several extensions John Schneider figures to consummate in the coming months as he presumably focuses on keeping the core of this Seattle team intact.

With no major free agents — Steven Hauschka and RFA DeShawn Shead will be the biggest — Schneider’s 2017 offseason will be more about setting up 2018 and beyond. And, if we’re lucky, he might do something about Seattle’s biggest weakness.

Some fans are giddy about the apparent salary cap boon of up to $38 million, thinking the Hawks can go hog wild on offensive linemen in free agency. But Schneider and contract specialist Matt Thomas know their 2017 offseason is really based on the 2018 salary cap — and they don’t have the flexibility fans think they do, assuming they plan to stick with their MO of keeping their own stars.

With Kam Chancellor, Jimmy Graham and Justin Britt also due for extensions in 2017 and a bevy of star defenders, plus Tyler Lockett, signed only through 2018, every move Schneider makes now has to be made with those players (or replacements) in mind.

Of course, what’s on the mind of most fans is the offensive line. Plenty of folks still want Seattle to trade for Cleveland All-Pro left tackle Joe Thomas or perhaps sign a young veteran such as Cincinnati’s Kevin Zeitler. And some think they have the money (and desire) to go after one of the top defensive tackles — Arizona’s Calais Campbell, Kansas City’s Dontari Poe or Carolina’s Kawann Short (if any of them reach free agency).

But those fans are getting a little ahead of themselves. Assuming the Seahawks want to keep most of their stars, they don’t have the ability to add more than one expensive free agent or a couple of mid-tier salaries. It’s less about the 2017 cap space than about how it all works in 2018 and beyond.

Before Bennett’s deal, OverTheCap.com had the Seahawks sitting $54 million under a projected $178 million cap in 2018. But the limit will probably end up a bit higher, around $185 million. It looks like Bennett’s 2018 cap hit will be close to $11 million, so that would leave Seattle with about $50 million, with just 30 players under contract entering the 2017 offseason.

If the Hawks were to pay Chancellor and Graham around $9 million or $10 million a year, extend Shead at $6 million, Britt at $5 million and Hauschka at $3 million, that 2018 space would quickly diminish.

Take out the usual $6 million reserve for rookie signing bonuses, practice squad and injury replacements throughout the season, and they could have as little as $13 million for 18 players to fill out the roster.

An RFA tender for Thomas Rawls — if he could stay healthy in 2017 — would take out around $3 million more. That would leave them just enough to finish their 53-man squad with a bunch of mostly minimum-salary players.

With all of that in mind, the only way they can afford to make any notable moves in 2017 free agency is if they don’t extend one of the aforementioned players or if they plan to make some cuts in 2018. The obvious possibilities there are Jermaine Kearse and Jeremy Lane, 2016 underachievers who would net $9.75 million in 2018 cap space.

That’s enough to pursue a good tackle in 2017. But don’t expect it to be 32-year-old Joe Thomas. Schneider has not shown any known interest in trading for the $10 million All-Pro, and the Hawks might decide to stick with George Fant as their lefty. Instead, Schneider might be inclined to try to add a younger, mid-priced right tackle — maybe Detroit’s Riley Reiff or Baltimore’s Ricky Wagner for around $7 million or $8 million a year.

The GM also is very unlikely to pay premium dollar (over $10 million) for a top defensive tackle — even if Russell Wilson might have been trying to recruit the 30-year-old Campbell after the Seahawks lost to Arizona last weekend.

Schneider’s successful MO has been to sign D-tackles for relatively cheap — e.g., Alan Branch, Tony McDaniel, Ahtyba Rubin. If the Hawks want an interior pass rusher, they’ll find a veteran bargain or look to the draft, which seems pretty deep at DT again.

Schneider knows he is going to have to draft some good defensive players in the next couple of years, especially with Rubin, Earl Thomas, Richard Sherman, Cliff Avril, K.J. Wright and Frank Clark all up for free agency in 2019. A few — if not most — of those guys probably will get extensions in 2018. But you never know what might happen: Rubin and Avril will be in their 11th seasons, and Thomas might consider retiring after his contract is up.

At this point, 2019 is a mostly blank slate — with only Wilson, Bennett, Doug Baldwin, Bobby Wagner, Jon Ryan, Lane and some current rookies signed. Schneider will start filling up that roster in 2017.

But every move he makes will be based on what fits in 2018 — and that’s probably not quite as much as some fans might think.