You will take your chances with Ebay stuff since you don't know how old it is and whether the activator is still good.
As well, to spray clear well, you need a good spray gun, not a cheapo Sears $50 job. Compressor must be powerful enough so that you can paint the whole car in one shot. Otherwise you need to mask off panels and do them in groups or individually.
And lastly, unless you have protective gear and a fresh air breathing system, I would not spray a two part poly-urethane clear with Isocyanates unless you don't care much about your health.
You would be better off prepping it by scuffing it with a 3M grey synthetic pad as already mentioned, mask as much off as possible yourself, and take it to a paint shop and try to get a deal. You might get them to do the whole car for $300-400 this way if the masking and prep is minimized for them. You will get a much better result this way since these guys can lay down a clear like glass. If you try to do it yourself with little experience, you will likely get a lot of orange peel and runs which will result in a LOT of wet sanding and polishing later. Better to try it on a buddy's car first.
dave mc