Hi Tricia,
Yes, I am a fan of nauture doing her own stuff. Mine had fry within the first few months of being in the new pond. Have never tried spawning mats - they seem to manage fine without.
As Anthony says, things will find a natural balance when it comes to quantity of fish. I was in a real quandry when mine had hundereds of fry as to what to do with them - neddless to say, many more died than survived, but its reached a natural level. the danger in taking them out and then putting them back later is that you could upset the balance by overstocking.
Here's a bit of info I I took on baord when first stocking my pond, and I kept it under the recommended amount to start with;
To assess how many fish your pond will support, estimate its surface area and allow 60sq cm of surface for every 1 cm of fish (equivalent to 24 sq. inches per inch of fish). Since fish grow and breed, it is best to start off with around one-third of the theoretical maximum number. For example, a 1.8 x 1.2m (6ft x 4ft) pond will, in theory, support 360cm (144ins) of fish, equivalent to 36 individuals averaging 10cm (4ins)long, but, in practice, you should have only about 12.
When it comes to feeding, you shouldn't really feed when the temperature drops below 10 degrees.
On additional plants, as well as the kinds you mention i have a lovely equisetum (probably wrong spelling!) which stays at about 2 1/2 ft tall, and I also have a few of the red lobelia - some people find them a bit garish, but I think they look great in summer. The lobelia is in my margins, but my mum had some which stays in pots around the edge - just keep well watered.
My filter is hidden by rocks and plants. Mine is 'bucket shaped' to start with, so i have it half sunk in the ground, and I have a sort of 'woodland rockery' around my waterfall and the back of the pond. I've strategically planted around it and have rocks hiding it, all with a bark mulch round them. [A slightly eclectic 'woodland rockery' as it also includes an acer and a banana!]. Various pots & plants etc, can conceal yours. I'll also post a pic when i get round to taking one...!