My CAA RT examiner told me to say as little as possible to as few people as possible. I think he was right, but I would expand on that to say there is little point in talking to anybody unless they can offer a useful service, and in practice that means radar.
So, non-radar I don't talk to. Equally I won't overfly some such airfield at 2100ft AGL
Conversely I do try to talk to any radar service.
The info passed should contain just the part of the route that is relevant to
them. That means avoiding waypoints already passed - unless the most recent one of them is essential to get across the routing. As for forward waypoints, I give 2 or 3 max. Plus of course dep & dest but those are in any initial radio call anywa (except following a handover).