Hau, Cameron, You didn't mention the age of your peach trees, except for the seed grown one.
Peach trees normally take seven years to first fruit production. You mention that your primary trees are only three years old, they are not yet mature enough to produce fruit to eat.
Cross pollination is a requirement for really good peach production, it does not change the taste of the tree's fruit, only the genetics of the pit would be affected. This is not always a bad thing.
I would plant the new, seed grown tree near the others and wait for it to begin producing fruit, at that time you will know what the peaches from that cross taste like.
Three peach trees is a good number for a small orchard producing fruit for personal consumption.
On this note, some of the best fruit orchards have a variety of trees such as Apple, peach, plum, cherry, fig, living in close harmony. Think " the more the merrier".
I would change the mulching components to composted manure blended with some standard
compost.
Be sure that any mulch is not touching the tree trunks, they need to be able to breathe clear to ground level.
Mulch touching the trunks tends to create problems with bark rot, insects and other nasties you do not want getting into or onto your trees.
This is the perfect opportunity to learn about fruit production from seed grown, cross pollinated fruit trees.
As mentioned before, if nothing else it can become rootstock for any other pitted fruit tree you want to grow in your orchard.