No shortcut for increasing font size
There is no shortcut to increase font size via a shortcut keyboard (like ctrl + + or ctrl + mouse whell) in Gedit, this could be handy. Geany, Builder and Elementary's Code use ctrl + + to increase it. It could be nice to have it on Gedit too, in particular because that way you can quickly try different sizes on-the-fly before find the best one for you.