If you already manage tags through Google Tag Manager, Orbit's script installs as a Custom HTML tag with an All Pages trigger — no separate code change on the site itself, since the GTM container is presumably already installed.
Not especially — Orbit's script only needs to load and execute once per page, so as long as the Custom HTML tag fires on All Pages, its order relative to other tags doesn't affect tracking accuracy.
No — that's the point of this route. Once the GTM container snippet itself is installed on your site (typically already true if you use GTM for other tags), you manage the Orbit tag entirely from the GTM interface.
There's a small delay, since GTM has to load its own container script before firing the Custom HTML tag, but it's generally well under the window a real-time count needs.
No — Orbit's script needs to execute in the visitor's browser to detect them, so it has to be deployed through a standard web container's Custom HTML tag, not routed through a server-side container.