Good morning!
I eat congee most mornings but usually a meat version. However the basic recipe is the same no matter what is added. Once a week I use my slow cooker overnight to prepare a week’s supply. It keeps well in the fridge or can even be frozen.
I find that different batches of rice require different amounts of liquid. I think this depends on the type and age of the rice. So when I get a new batch I experiment. I start by using 1 part rice to 6 parts liquid- mostly water but sometimes chicken stock, although you could use vegetable stock if you want. Additions at his stage are only salt, if you want to go that way. Most congees here, however are unsalted with any salt component coming from the other additions, especially the pickles. But then, salt is rarely used with rice, which is seen as a neutral background to other foods..
Next morning, I check it and should it be too thick, simply add more water and cook a bit longer. You can’t really overcook congee unless you get ridiculous. If too thin (rarely) then a brisk boil thins it down. Obviously what you think is too thick or too thin may be different, so is to your own taste. Next time I use that batch of rice, if not at first how I prefer it, I adjust the starting amount of water next time. It is always somewhere between 1:4 ad 1:8. The breakfast places with congee on the menu usually offer two or three consistencies.
I then decide each morning what I want to add. This is most often meat (pork or chicken) and century eggs. These I quickly stir fry with perhaps chilli and ginger and add to the cooked rice. Then serve it, almost always with some pickled vegetable.
Another favourite which is vegetarian is mushroom congee, usually made using fresh shiitake mushrooms but any fresh or rehydrated dried edible mushroom would work.