18 litre pots are ideal for partial mashing, small all grain batches and extract brewing.
Because of the size, you can get away without using a chiller, just dunk the whole lot in a tub of water in the laundry, change that a few times to chill the wort. Make sure the handles are firmly attached.
If you decide that you want to launch into larger batch sizes, you will still use the 18 litre pot from time to time, for heating sparge water, and boiling part of the mash for decoctions.
Every house needs a large saucepan for big batches of soup, and cooking plum puddings.