Good ideas! I agree vermiculite for starting plants, perlite for making the medium lighter and more well drained. With coarse horticultural grade perlite you can make your own potting soil from equal parts of perlite, fine pine bark mulch and peat or coir.
Around here the nurseries last year were all supplied with fine non-horticultural grade perlite--a sticky useless white dust. So check that what you buy is coarse horticultural grade perlite.
