I bought a good chunk of my initial dive gear on eBay back in 1999 and 2000. It was an excellent route to go. I have since bought new gear over the last year or so (mostly through local dive shops). There is nothing wrong w/ eBay or CL, but it is more of a buyer beware. You noted you have 5yrs xp on eBay, so you know some of the games/tricks.
I would lose the spare air for now. Get thru your lessons and then you can look at that. Even if you got the spare air, it is incredibly unlikely that you will have it with you through your lessons. You will also be diving quite conservatively in class so needing spare air will be highly unlikely. Even if your buddy tweaks out, the instructor or divemaster will be right there to aid you. If you are trying to cut costs, lost the spare air for now.
The Air Source is a solid option. I have the air source and an octo for my classes. I pull the octo off when I go fun dive, but for classes, I want to have the octo so my students know where it is and they do not freak out when they see my gear "missing" an alternate (when in fact the Air Source is there the whole time). If you go through your training dives with this gear, you will be fine. You will get practice with support and should feel comfortable with it by class-end. If not, maybe you can ask the instructor for a "quickie" pool session.
I would probably go with BCD, reg/alt, and computer for your first setup. Getting the computer now is another thing as noted above... if you train with it now, with supervision, you will be stronger with it later.
I would also have all things serviced. If you talk to the seller, and feel comfortable with them, you may get them to cover servicing, or lower pricing to off-set it a little. You should have it all checked out before doing too much with it.
As for product choices, those are all good ones. The Black Diamond is a good BC. I prefer the (Seaquest) Balance, but since it sounds like you have a solid deal potentially in the works on the Black Diamond....
I use the Legend ACD LX reg as my backup (it is my wife's primary when we vacation) and we are both happy with it. It tends to give a little dry-mouth though, just fyi. I was not bothered by it, but my wife who has very few dives under her BCD has noted it to me a few times. It is a great reg though.
Good luck, get the gear you like at a price that makes you happy and get wet. You will learn your gear quickly in your class. If you do go with the Air Source, point it out to the instructor.. sometimes they may miss that you have it and not remind you and your buddy about different techniques for out-of-air scenarios, etc.