Kat - your loquat seedlings will make good rootstock for the excellent cultivars Darkman has at his place.
Darkman - wow, you're more fruit crazed than I am.
Quince can be a vigorous rootstock for pears and offers fireblight resistance.
For the spacing of my trees, I was shooting for 10' on center. After the installation of the perimeter walls I had to compromise to 9.5'. I train my trees with winter and summer pruning in accordance to "How To Prune Fruit Trees" by R. Sanford Martin. I also control the height to 8' by periodically thinning out taller branches.