Since I can't advance mucj during the week (yeah, work) I've took the time to learn about some things which relate to the project.
Font rendering quality
I've been using Adafruit's GFX library for rendering fonts on the SSD1306 and I was really disappointed by the rendering quality of self converted TTF fonts. It seems that it isn't so easy to convert vector fonts to bitmap and expect them to look nice on 1 bit displays.
When I used NuttX I had a better experience with don't rendering and I realized it used bitmap fonts, which are generally hand made and thus look really nice on these kind of displays. There are several formats for bitmap fonts such as PCF. The nice thing is that freetype library can read it and thus I could use the same fin convert utility from Adafruit. When I get the chance I'll test it but I suspect it will look much better.
Battery re-charging and permanent settings storage
I started with the idea to leave out battery re-charging in the device since I couldn't find any SMD ICs locally for that and did not want to include Chinese modules to the PCB. This meant that I would loose settings on the device when taking battery out for re-charging.
Since the STM32F103 does not have EEPROM un thinking on adding a cheap I2C or SPI chip for that.
However, I found a local distributor which has many nice SMD components and found that it sells several re-charging ICs. Among those, I found the MAX1555 and MCP73834.
Thus, in trying to decide if it would be worth to add this feature after all.
If anyone has any opinion about that, it is welcome.