Joe,
Your list for the G3X looks good. From what I have read you will need the WAAS GPS-20A for the GTX-45 to work for ADSB out.

These are totally preference items:
I chose the panel mounted GTR-200 radio with the display and knobs. I like having the display and ability to tune, flip-flop frequencies and activate the "monitor" function without having to do it through the G3X display which can involve a lot of button pushing and take you away from other important stuff on the MFD. FYI the monitor function sort of makes it like a second radio, I use it to listen to AWOS without going off the primary frequency.

Also it looks like most of the functions of the GMA-245R are included in the new GTR-200B. You really don't need an audio panel unless you are going to have more than one COM.