I have always had ponds about me. My childhood was always spent in cooee of water life.
It's not that I'm into fish and aquariums in a big way -- but I like small bodies of water: billabongs, dams, waterholes, lagoons....
I've used water filled plastic buckets, terra-cotta pots, laundry sinks, baths, old tires, and gar bags to sustain my obsession with pond-hood.
A house without a pond -- a water feature -- is missing something.
It's unnatural. Not a home.
In the sub tropics where I exist you live and learn and my absolute primary rule is that it is better to have many small ponds rather than one big one.
Big ones I've had. (I've turned a swimming pool into pond). But big bodies of water are a management headache.
Aside from the problem of keeping water up to them -- not easy if your water supply is chlorinated and chlorine kills fish -- ponds are, regrettably, cane toad magnets and the first law of pond management is:
It is easier to cull toads from puddles than not.
That's the trick. Indulge yourself with water by all means, but do it in small doses. If you have ever hunted toads by torch light at night and fear the infestation of your cherished waters with their poisonous eggs and tadpoles, you soon learn to keep your search and destroy patches small.
At present I have four ponds in various locations in my garden. One is formed by a plastic pot, the rest are old car tires with plastic bag inserts.
Car tires make great little reservoirs. I remove one side of the rim with a Stanley knife and pad the shape with some strong gar bag material before throwing in some potted water plants and adding H2O.
While I grow edible plants in these ponds --Watercress Nasturtium officinale and Water Spinach / Kangkong Ipomoea aquatica -- I value the life aquatic as an enrichment of garden ecology.
Note on 'small fish': the complication is that they may/will eat frog's eggs. There is less chance of that with small native fish species but I haven't had much success keeping Rainbowfish.However, when locating your smallish ponds remember that frogs do what frogs do and a night time croak can be cause for insomnia. Much as I love Striped Marsh Frogs their staccato 'dup!' drives me crazy. So don't put ponds near bedroom windows. In fact put them a long way away from the house.
When designing your pond, also make a point of adding sticks or branches as hardware so that the frog can get out of the water. They need their pathways.
Also consider that many local species prefer shallow water to deep ponds and appreciate vegetative cover as much on the bank as in the water. While you wait for that to grow, throw in some Azolla (although goldfish will eat this water fern gluttonously).
Ponds also cool down the locale and give you the chance to plant out the bank with grasses and explore stunning florals like the Louisiana Iris and water lilies.
Where I now live I have tank water and that makes water level top ups so easy to do. Chlorination of water supplies is a major handicap to pond management and for a serious pond habit you need rainwater ... on tap.
I used to try to force my ponds to attract more than amphibians and insects, but while the dogs will drink out of the ponds (despite my discouragement of the practice) they don't suit birds despite the sticks I may run along the water's edge. If you want to hydrate the local avifauna use a bird bath. Birds prefer to drink above ground -- as it is safer/away from predators -- from an easy to land on lip -- and like the wheel, there's no reason to stress out and try to re-invent the bird bath.
Make a bird bath: upturn one longish terracotta pot and place a flat terracotta dish on top. Voila! Instant bird bath.
Our bird bath is so muti species popular that I make it a practice to change the water every day as it serves as both a drinking and a bathing station. Compared to putting wild out bird seed, bird baths attract a better class of personnel...
Ponds are preferred Cane Toad habitats. To combat this, you could raise your pond up -- I think at least 50 cm high -- above the surrounding ground as Cane Toads cannot jump like native frogs. But that means that your pond will lose a verge option and your water may evaporate more quickly as it will heat up faster in Summer. Another option is to fence your pond...a fence of verge grasses is effective against Toads but then you won't be able to see the water.
Rainbowfish: If you do put Rainbowfish in your pond make sure the species you select is indigenous to your catchment. Just in case. There are enough feral stock in our waterways and you don't want to upset the struggling Rainbows any more than they are challenged. If your local creeks have guppies in profusion -- and most Brisbane water ways do -- I reckon you can use those as your mosquito control preference. They aren't as effective as Rainbows but they are already occupying the neighborhood. To protect your frogs harvest from the fish, remove any eggs to a isolation trough.