Getting something for these functions, is one of my tasks this spring.
I'm leaning towards a tablet for nav/gps functions and a separate depth unit with it's own display but with NMEA output that could work with the tablet. At least that's the goal.
While a combo unit has it's advantages, I'm not a fan of a single point of failure.
As for a compass, I'd just get a hand bearing compass. Pre GPS, I used it 99% of the time, over a conventional mounted one. It's a puck style one that hangs around my neck, so it was always ready for use. The possibility of losing it overboard makes me want to have a standby.
Of course, the amount of gear you need depends on where you sail.
Many C22 sailors just need a depth finder, if anything. If I was always sailing a lake with line-of-sight navigation, that had a soft bottom, and relatively consistent depth.... I'd not have anything at all. Just like when sailing a dinghy.