I like your website. Good luck with your venture. In an effort to help I thought I'd add some thoughts. about junipers to add to your line up. I looked at your list of junipers and added some notes on each.
Above all I would try to source some Juniper chinensis varieties 'Kishu' and 'Itoigawa' as these are the two best cultivars of J. chinensis used for bonsai. They are easy to root via cuttings, if you can't find them in wholesale quantities get a few stock plants for yourself and every summer, strike a new set of cuttings in August, they will be ready for sale in 24 months, no winter protection required in Chicago area. I leave the cuttings with no roots outside in their flats all winter. Roots form over the spring-early summer and growth will begin in August. By their second August they will be established enough to sell.
You have a number of Juniper chinensis varieties on your list, which are all essentially varieties of Shimpaku. I would only add the ones that offer something different, like blue foliage, which you can get from 'Blue Pfitzer' which makes decent bonsai. The 'Pfitzer' types or hybrids are popular for bonsai in Europe.
Juniper horizontalis, obviously makes a good cascade, though they are slow to trunk up. Nick Lenz used horizontalis to make upright trees with decending branches much like a spruce or fir. Very convincing. Consider adding at least one of the horizontalis cultivars. I prefer the blue color foliage. I have J. horizontalis from the Waukegan Barrens, and it is a nice purple bronze all winter, and mostly green in summer.
If you add 'Grey Owl' or 'Hetzi Columnar' keep in mind seasoned bonsai people will avoid them because they are thought to be J. virginiana hybrids. They will submit to bonsai cultivation better than J. virginiana, but they may still be a bit of problem. The "pure type form" of J. virginiana has a bad reputation as a bonsai subject. Vance Hanna and a few others have turned out good trees, but they are the exceptions. rather than the rule.
I hope my notes below help a little
BAR HARBOR - horizontalis - prostrate - can bronze some in winter, blue-ish in summer.
BLUE CHIP - horizontalis - prostrate & quite blue
BLUE RUG - J. horizontalis 'Wiltonii' - a prostrate juniper cultivar fairly blue.
BLUE PACIFIC - shore juniper - J. conferta - needle foliage - only hardy through zone 6, according to MOBOT.
BLUE PFITZER - J. chinensis or a chinensis based hybrid, foliage like a Shimpaku - pretty good for bonsai, normally scale foliage, does not revert to juvenile very easily, though it will if over-pruned. Officially J. x pfizeriana "Pfitzer Junipers" are hybrids of (chinensis x sabina)
BLUE STAR - J. squamata - needle foliage, good blue color. More upright.
GREEN SARGENT - better would be to source 'Itoigawa' or 'Kishu' Shimpaku, Green Sargent is a more coarse version of Shimpaku - J. chinensis.
GREY OWL - purportedly a J. virginiana cultivar, many suspect it is a hybrid, because it is much better behaved for bonsai than J. virginiana.
HETZI COLUMNAR - another cultivar of J. virginiana, this one found in Missouri. Needle foliage on young branches, quickly reverts to scale foliage as branch ages. Vertical growth habit. Some consider it, a hybrid (chinensis x J. virginiana). Behaves better than "pure" J. virginiana as bonsai. Some consider it J. x pfizeriana (chinensis x sabina) in which case it was an "invasive species" as the x pfitzeriana types are a European hybrid group.
PARSONI - J. davurica - used to be thought a variety of j. chinensis - grey-green scale foliage, not as tight as shimpaku, but can reduce well enough for even shohin bonsai. - low and wide growing, not upright.
ROBUSTA GREEN - a cultivar of Juniper chinensis, essentially an upright, slightly more coarse growing Shimpaku.
SEA GREEN - wider than tall growing Juniper x pfizeriana - hybrid (chinensis x sabina) - usually scale foliage, like a coarse foliage Shimpaku
TORULOSA- a cultivar of J. chinensis 'tortulosa' sometimes called 'Hollywood Juniper' - a form thought to have been discovered in California, noted for contorted shapes. Not a prostrate plant, wider than tall, though it can grow upright to 15 feet or so. Alleged to "trunk up" more quickly than some shimpaku types. Usually scale foliage though can revert to juvenile foliage as with most Shimpaku types.
