Re: Homebrew from scratch #ubitx
Several have explored modules for BiTX/uBiTx. Paul M0XPD is one: http://m0xpd.blogspot.com/2014/08/plug-in-bitx-modules.html
ON6RF developed a very nice PCB with all the modules able to be snapped off, thy had their board on Oshpark or similar, http://soldersmoke.blogspot.com/2017/10/modular-bitx-boards.html
I think modules are a great idea, because I like to swap variants. Separate point to point wiring between them should be avoided because it defeats swappabiilty. The idea really makes sense when you think of with a backplane/motherboard with all signal and power connections, and pluggable modules separated by screens where necessary. 0.1" headers work at HF. The module boards can then be vertical. Surface mount allows them to be tiny.
Regarding scratch building Raduinos, I have built 4 or 5, using a Nano, veroboard or hand drawn PCB, and the Adafruit si5351 breakout. All of mine are implementations of the Raduino circuit so I can run any of the community's software.
You might get some ideas here and here :
73 Paul VK3HN.