Planning Summer Revamp Of Pond

[three-fingers]

First off, I made a previous topic about my pond here, but since then I've estimated the actual volume of the pond using maths (originally I just made a guess) and its a tad bigger than 50gals, at ~100 uk gals . I've attached a picture of it in its current state, and a bad diagram of what I'm planning to do with it on microsoft paint.

I would really like to be able to have a couple of goldfish in it, and I'm planning to either be heating it with a 300w heater during the winter, or if for some reason that doesn't work, the goldfish could be moved into a small indoor tank for the winter (although that may not be an option depending on how far we are with the house by winter).

I plan on buying a large pond pump, and using a few of the largest sponge filters I can find attached to a plant pot in the pond.

The pH in the pond is 6.8 - 7.5 depending on the time of year, and it has lots of 'oxygenating' plants.

So far, the only creatures to take up residence in the pond are 3-5 frogs and some large ramshorn snails.

Questions:
Does this sound OK for a couple of goldfish? (probably rescued ones)

After cleaning it out and setting everything up, how long should I wait before adding any fish? I'm presuming the pond will cycle the same as an aqaurium?

Is it legal to take introduced fish like minnows (Pimephales promelas) from the 'wild'? There's a dirty small pond nearby that has some minnows in it, and a canal that has them too (though the canal may have the native species which is probably less suitable). If goldfish are completely out of the question, I'd settle for something like that, hopefully I wouldn't have to heat it that way either .
I can buy rosy red minnows (which are the same species but a different colour) from one of the garden centres around here, but while it's legal to keep them in indoor aquaria, apparently you need a licence to keep them in ponds. So I'm not sure putting 'wild' caught ones in my pond would be legal, and even if it was, surely the rosy red minnows would be better? Since they have more of a chance of being eaten if they somehow got into another water system.

Thanks for any input!

Here's the pond in it's current state:

And here's the very rough diagram of the pond:

 

[GoldLenny]

Using this site, http/www.fishpondinfo.com/calc.htm, for a round pond and your measurments, but approximating the diameter at 5' and the average depth at only 1', your pond has 146G US or 122G UK. Using 4.5' diameter with 1' average depth, your pond is still around 120G US and 100G UK.

With unusual shaped ponds, the only way to know precisely would be to drain it and then refill it with known measured containers like a garbage can with a known volume. You could also come up with a pretty good estimate of your flow rate out of your hose by timing how long it takes to fill up a 5G bucket. Do the 5G bucket test a couple of times and pour the water into your pond. You will now know how long it took for 10G to come out of your hose. If both times were the same, then you can just run the hose at the same volume and time the filling process to know how many gallons it has.

Presuming it's at least 100G, you could probably have two long-bodied goldfish but go for comets (or comet shubunkins) as they stay a little shorter and slimmer so they would be less bioload... as long as you add some kind of filtration. It doesn't have to be much. A simple pond pump powered fountain or waterfall or frog spitter, etc., with a DIY prefilter (like I have detailed on my blog) will work wonders for the overall ecology of your pond.

 

[three-fingers]

OK cool thanks .
I'm pretty happy I can have goldfish now .