There is no growth chart as the colours and features your baby inherits is random and there are far too many possibilities to reasonably list.
The only generation where your care effects it's growth is the 1st one, and on the Sanrio version it is identical to the Spacey and Melody versions.
I have seen it done before. I forget where i saw this, but someone added an LED to their Tamagotchi that lit up when it made a noise. I have also seen backlight mods for both tamagotchi and digimon digital pets.
However, what you are describing would require you to solder an LED to where the...
I'm pretty exited for Splatoon 2 and Pokemon Ultra Sun/Moon, and I am looking to check out the new sonic game that is coming out this year. I am also following the development for the Legend of Bumbo: Sewers of Dross.