Layering substrate does not work very well, it will get disturbed, mixed... and then the peat will drift all over the tank. :-(
Also, peat is so light that gravity will pull the Flourite or EC under, and again, the peat is exposed to the water column and will drift around.
1st layer: dust in the peat so you can still see the bottom of the tank. Or skip it entirely.
Also in the first layer: Osmocote, other tablets
2nd layer: A single product like Flourite, EC or whatever you want.
If you want the black water environment that peat creates, add it to the filter.
I have removed as much as 25% of the filter media from a well cycled aquarium and had not issue at all with the donor tank.
I have set up and fully stocked tanks by taking a little media from each of several tanks.
Filling the filter with well cycled media provides about 50% of the bacteria that is normally found in established tanks. More bacteria live on the leaves, rocks and driftwood. The plants are also part of the biofilter. If you are taking the decorations from an established tank there will be some bacteria on them, but not a lot compared to the filter media.
Net result is that a well planted tank, with a filter of used media can usually be fully stocked with a reasonable fish load the first day. In fact it is better. The bacteria would die out without a source of ammonia, so lightly stocking, or running it for a week or so without a source of ammonia is a bad idea.