When requesting multiple VMs through the API, a priority can be assigned. The lower the priority integer, the higher the urgency:

# Request a VM with the highest priority (default priority is 1000)
curl -X POST "http://anka.controller/api/v1/vm" -H "Content-Type: application/json" \
  -d '{"vmid": "6b135004-0c89-43bb-b892-74796b8d266c", "count": 2, "priority": 1}'

{
  "status": "OK",
  "message": "",
  "body": [
    "c983c3bf-a0c0-43dc-54dc-2fd9f7d62fce",
    "e74dfc0e-dc94-4ca2-575e-3219ac08ffa2"
  ]
}

Nodes are constantly asking for tasks in the Controller. They will send a payload with information about what Templates/Tags exist already and the Controller will use that information + the start VM task priority and determine which task is right for the Node. If nodes that do not have the Template are getting tasks and having to pull all the time, you should consider using groups and placing these nodes in a fallback group. Then, tell your jobs to target the non-fallback group and they will prioritize the nodes that have the templates.