zachi-
I'll give you some advice, but maybe not what you wanted. I've seen the offerings of the bamboo seeds you listed on eBay, and most of them come from outside the U.S. If so, you're violating federal importation regulations, and possibly exposing U.S. strains of bamboo to diseases. Those regulations apply to both bamboo plants and seeds.

Having said that, your bamboo should do fine in your Zone, but it will take many years for the seedlings to get full size. I have some bamboo started from seeds 4 years ago and they're not 3' high yet. If you're interested in having decent size bamboo you should be buying potted divisions, or trading with other bamboo collectors, which is how those of us who are bamboo nuts get most of our plants. Growing from seed is a fun sideline, but it takes a long time, and, since bamboo flower and put out seed very infrequently, you can't find seeds for most species as you can for other plants.

Here is a link that might be useful: Bamboo import and quarantine