What you are referring to as 'the bumper', is actually just a plastic cover. If it's appearance doesn't bother you then don't worry about it, no safety issues whatsoever.

All the things you describe are merely coverings or trim, the bumper is only there for show these days and most of the time held in place with no more than half a dozen plastic clips.

Do not involve your insurer, none of these things are in least important or worth reporting, unless you really want to pay more next year because they deem you a risk, and yes this is what they will do.

In practice it sounds like a an hour spent on the usual auction site would source all the parts you need, if you can't fit a new grille or trim yourself, then no doubt a handy local garage chap would soon pop them on for you, a new number plate would cost around a fiver.

If the bumper is still solid and the clips securing it are not broken then i wouldn't worry about it, you could glue the split up, then paint over it if it bothered you, or you could find a used bumper but finding one in your colour could be a challenge.

None of these things are desperate, unless the trims or bumper are falling off or any of these cracks/splits have left sharp edges which would be a danger to pedestrians, if they are remove or gaffer tape the sharp edges temporarily and carry on driving until you can get the parts to fix.

WBAC or similar will knock the value a lot for these body defects, so i'd fix the present car if its a good one otherwise.