Ok, now i received a tinyrtc module from China. Seems like i did pick bad choice; this version requires +5V to work. And on top of that its made for LIR2032 rechargeable battery, and the China shop shipped it with "rechargeable CR2032", that i belive to be just normal CR2032. To avoid any troubles, i soldered some components of (include +5V pullups on the I2C bus) as described here:( source: google gave me this but i think i found it on some discussion thread)

While getting the chip connected i first tried with GPIO16, but it seems like (after googling) there is something special with that pin, using pins 14 and 12 works fine.

Anyway, i need +5V rail for the HC-SR04 and LM35 so its no trouble. The (adjustable) buck-converter have not arrived, when it does i have all the components i need to make first proto board. I'll use the buck-converter to power +5V and then use linear regulator to get the 3.3V for the ESP.

I also managed to use the platformio data/ folder, that works fine as long as you remember to call SPIFFS.begin() before assuming anything to work. I dumped CSS and index.html file there and i am using the C++-code to provide json - get api for the static html. This way i do not have to hardcode any html to the C++ side, which is nice.

Here is screenshot of the current main page. Simple.