To drain your pond you will need a pump attached to a hose to suck out the water. Any city water will need to be treated w/Pond Prime by Seachem or something similar to remove chlorine/chloramine. You'll need some kind of filter too. Frogs will come and go as they please.
There are some pretty goldfish out there. I like Shubunkin goldfish as they have patterns sometimes similar to koi w/the different colored areas.
I see our house Queen of the OTG has already been here; good advice all. You don't need a bottom drain, so don't worry. To keep mosquitoes from breeding, have water movement of some kind. That fountain you mentioned would have had that effect. If you want low maintenance, goldfish don't really need to be fed unless you like doing it, as long as you have some plants and let algae grow on the sides.
Once established, DON'T powerwash/wash the pond down thinking you're helping. If excess mulm/debris/muck, then shovel/rake/net that out slowly IF you have fish in there already so you don't stir the bottom up. If empty of life per se, go to it!
Good that you checked to be sure it holds water; a lot of other problems can be fixed after the fact but not always a leaking pond!
Think on if you want to install a bog filter (lots and lots of info; just do a search here) because once established, you don't have to do anything except thin plants now and then. And it's both cheaper and better on the eyes than anything store bought, imo.
You don't want koi, as J.w says; koi can grow to over 30" easily. They require 1000 gallons for the first and 250-500 for each addtional, more or less. Goldfish like shubunkins are the poor man's koi and are great! They won't get nearly as large.
Too, your pond is shallow(er) so depending on where you live, you may have winter issues. Let us know and we can advise re that topic.
And if no one else asks, we LOVE pics! So, be sure to keep us in the loop as we love to
spend other people's money and watch help!
