Food for thought, and just an example, but you could buy a GRT Sport EX for $1500, that includes basic engine monitoring, an echoUAT ADSB-IN/OUT unit for $1400, and a used GTX-327 for about ~400 these days. A GTR-200 gets you a great comm radio and intercom system for $1400.
That system would give you a full MFD with mapping and engine monitoring, ads-b in and out, and a comm. Want an A/P later? Just add servos, the GRT has built in AP functions.
Lots of other combinations you could do, and different manufacturers, but I think you may be unnecessarily limiting yourself.