Adding extra sensors

I do research in remote medicine and have built multi sensor platforms for use on expeditions/refugee/disaster zones etc.

I think Meshtastic lives up to its name and is definitely fantastic with the testing I have done over last week.

I am looking to possibly utilise Meshtastic and add extra sensors to some of the commercial lilygo boards, to collect physiological data and send summary data at intervals. Possibly also add some sort of menu screen and different button operations. This is strictly for non profit.

I have extensive Arduino experience and can normally work bits out. I have cloned the platformio but it seems bits are very broken down and I can’t get head around the order the code runs. I have read the bits about creating a new board and changing pins but for now it is more about adding in code to an existing board and tweaking some minor bits like GPS frequency etc.

Is there anyone who can give me a little direction. Just a paragraph or two of where the main wrapper code is so I can add in sensor readings etc… Maybe also where to find bits on screen and button operation.