You could use something like the Aera 660 to drive your non-Dynon auto-pilot (e.g. TruTrak) and link the 345 via serial or Blue Tooth to the 660 for wx and traffic.
If you have a Dynon system, you would want the Dynon AP servos, transponder and GPS 2020 antenna plus the new ADSB-472 for an IN source of wx and traffic.
Lots of Q&A on the ACS site, where the ELT question has already been posed.
Q: My ELT (an Artex ELT 345) needs GPS position information via RS-232. Can the WAAS-equipped GTX-345 supply that information via one if its serial ports?
A: Garmin recommends connecting your ELT with a GPS such as the Aera 660 or GTN 650.