It depends what you are going to grow in it.
I take it its the old fashioned white sink you've got.
A variety of Herbs , Type of Herbs to plant is , Chives, Marjarom , Thyme, Parsley (this is not a hardy plant, but the others are), Garlic Chives , Sage , Basil(not hardy either)about 8 varieties should be ok with this type of plant.
Pinks (carnations), Day Lilies, spring bulbs (planted in the Autumn), Nasturtium, Fuchsia's, Lobelia , Busy Lizzy, Petunias,Nemesia, Ageratum, French Marigold.
If not wjhy not try salad
Little gem lettuce, Tomatoes, Radishes, if not try Dwarf french beans, I hope this will be of some help

Sorry i mis read your question Great , 3 or 4 plants should do if you are doing a sink pond,
if not you could always do what i have written above

Oh Hijuju lol Thanks Want a wildlife pond

I had a washing up bowl as my first pond until I decided I wanted a larger one. I would suggest an aerotor and that's about all. I found 10 or more newts and one frog in mine when I moved the pond. Amazing where they come from. In my larger pond, 3' x 3' I have over 25 newts and two frogs my oldest did not survive this winter. Also I know damsel flies visited and laid eggs because we watched them. Good luck.

PS get the aerator from your water garden centre. They are usually most helpful.

Does it make alot of noise? I worry about electric in the garden