how to identify first element in array of node objects?
$nodes is keyed by the node ID, which you probably won't know in advance. Instead of directly trying to access the first node in the array, iterate over them with a foreach loop.

function mymodule_node_load($nodes, $types) {
  foreach ($nodes as $nid =&gt; $node) {
    if ($node-&gt;type == 'basic_page') {
      ...
    }
  }
}