Thanks. I reviewed all these documents and schematics. Things to note and new questions:
1) The USB/Ethernet LAN9514 chip (Pi 3B) uses a USB interface (not rMII ethernet PHY ) to connect to BCM2837 - section 9.4 of CM3+ specification.
a) These would connect to SoDIMM pins 165 (USB_DP) and 167 (USB_DN).
b) The LAN7515 chip (Pi 3B+) is custom for Pi Foundation, no datasheet or pin-out is available - you can't
buy LAN7515 for your own designs - any alternates (besides LAN9514)?
2) The CYW43438 WiFi/BT chip has a SDIO interface for Wifi and Serial interface for BT.
Per section 9.1.4 of the CM3 specification, SD1 (SDIO) is used to connect the WiFi (GPIO pins 34-43)
a) Per the CYW43438 datasheet, there is a 4 bit and 1 bit mode for SDIO. Which is used by the Pi WiFi driver?
Simply hook up all 4 data pins and don't care which.
b) Is WL_REG_ON used? If yes, where does it connect?
3) For CYW43438 BT component, a UART serial interface is needed.
a) It can be 4-wire H4 (TX/RX/CTS/RTS) OR 3-wire H5 (TX/RX/???) -- which is used?
b) Looking at Pi 3B header pinout - Console UART for Pi 3B/3B+ assigns /dev/ttyS0 (mini UART) TXD1/RXD1 (GPIO 14,15 ALT5)
For BT serial interface, /dev/ttyAMA0 is used (PL011 UART) TXD0/RXD0
So GPIO pins 30-33 (function ALT3) are used to assign CTS0/RTS0/TXD0/RXD0 - ALT3 is set by device tree?
c) Is BT_REG_ON used (reset)? If yes, where does it connect (which GPIO pin)?
d) Are BT_DEV_WAKE or BT_HOST_WAKE signals used? If yes, where are they connected (GPIO pins?)
e) Are BT_PCM_xxx signals used? If yes, where are they connected? (guessing not used).
Note that these chip connections for 2) and 3) above are not shown on Pi 3B or 3B+ schematics, so I had to infer from other forum posts.