MetrixWire APM

No — and you don't need to create one by hand either. One click on the connect screen sets everything up. The account has no email or password until you add them under Account, which you only need if you want to sign in on metrixwire.com directly or recover the account later. If you already have an account, use Sign in instead on the connect screen.

Nowhere. The plugin uses the hosted service at metrixwire.com. If you run MetrixWire yourself, point the plugin at it with define( 'METRIXWIRE_ENDPOINT', 'https://your-instance.example.com' ); in wp-config.php.

No. Connecting, reading issues, changing settings, managing alert rules and checking plan usage all happen in wp-admin. The Open MetrixWire button is there when you want the full dashboard, and signs you in automatically. Changing your paid plan is the one thing that leaves WordPress, because checkout is handled by the payment provider.

Yes. Define METRIXWIRE_KEY, METRIXWIRE_ENDPOINT, and optionally METRIXWIRE_ENABLED as constants in wp-config.php — they take precedence over the saved settings, and the fields they cover are shown read-only. A site configured this way traces without connecting, though the in-dashboard screens still need a connection, since reading data back takes its own credential.

SAVEQUERIES must be defined as a constant in wp-config.php; WordPress reads it before any plugin loads, so it can't be turned on from a settings screen at runtime.

Traces are sent on the shutdown hook, after the response has already been sent to the visitor, over a short-timeout non-blocking request. Failures to reach MetrixWire are swallowed silently. The admin screens cache what they read for a minute, so browsing them doesn't hammer the service either.

Anyone who can administer this WordPress site — the screens require the manage_options capability, and the Open MetrixWire button signs that administrator into the connected account.

Yes. Each site connects separately, keeping its own project and credentials, and uninstalling removes those from every site in the network.

The site stops tracing and its credentials are removed. Your MetrixWire project and its history are kept, so signing back in later picks that project up instead of starting a new one.