GET API，返回结果，如何发布它们

Question

I have been issued to call this API from a Car company and post it to WordPress posts with custom fields. I can successfully call the API in postman, below is the code I have generated from Postman. My next stage is to connect to WordPress and send this data so that each post will have one full set of information about said car. My PHP knowledge is rather basic, I believe I will be using the wp_remote_get and wp_remote_post, utilizing the REST API in order to get started what would you suggest I start with. Do I create a plugin which then runs in the background, or do I create a theme with Functions.php I am unsure at current what would be the best working practice. I understand this is probably vague but after researching and watching videos, all are using API feeds which don't require authentication. So I am a bit stuck, any advice would be fully appreciated.

        <?php

        $client = new http\Client;
        $request = new http\Client\Request;

        $request->setRequestUrl('https://api.****.net/APIv2/Vehicles/StockList');
        $request->setRequestMethod('GET');
        $request->setQuery(new http\QueryString(array(
        'stockListOptionModel.includeusedvehicles.includeImageDetails.includeVideoDetails' => 'true'
        )));

        $request->setHeaders(array(
        'cache-control' => 'no-cache',
        'Connection' => 'keep-alive',
        'Host' => 'api.***.net',
        'Postman-Token' => '79e50f16-0d32-402e-9586-34d7bc8fc590,0741d89a-02d8-4b50-8633-0f3c2eba8c1c',
        'Cache-Control' => 'no-cache',
        'User-Agent' => 'PostmanRuntime/7.15.2',
        'Content-Type' => 'application/x-www-form-urlencoded',
        'Accept-Encoding' => 'gzip, deflate',
        'OrganisationalUnit_UID' => 'a3db2a66-***-4ac2-a78a-0f042aab50af',
        'Password' => '***',
        'UserName' => 'api@*****.co.uk',
        'Accept' => 'application/json'
        ));

        $client->enqueue($request)->send();
        $response = $client->getResponse();

        echo $response->getBody();