Its perfectly legal to buy and own grow boxes. You can't be busted JUST from buying one!
At worst someone could find out you bought one, and then do additional surveillance to see if you're using it to grow something illegal, and then, if you are, bust you.
While not zero, I think the chance of that happening is pretty slim.
In the late 80s (I believe) the Feds got the complete purchase list of individuals who purchased "Phototron" units and then went after each one looking for MJ grow ops. People *were* busted this way, though I don't know if it was because they let the cops in (stupidly) to look around or because the cops used the purchase of a Phototron as "probable cause" to get search warrants. I remember reading about completely innocent orchid growers having their doors kicked down, so I suspect it may have been the latter.
But times have changed now, and there are many more places selling these sorts of things. It would be impossible for the Feds to monitor all of them, and in fact, I'd imagine many of these places don't even keep customer lists. If you were to do your order in a way not easily traced back to your grow area, I think that would greatly reduce any chance of a bust that way.
Personally, I'd say its probably better to just build your own grow box (if you can) since you'll do it cheaper, and will end up with something built exactly to your specs.
On seeds, the crime is possession of the seeds, not purchase. In theory, if the Feds could prove you were trying to purchase seeds, they could try to get you on "conspiracy to cultivate", but that's a hard charge to make stick absent other strong evidence (like evidence of possession of a "Phototron"!).
In general, the biggest risk of buying seeds from abroad is that they'll be confiscated by customs and you won't get your order, not that the Feds will bust down your door.
If customs finds your seeds in the mail, their policy is just to confiscate the seeds, and send you a harshly worded letter indicating that someone mailed you contraband and they seized it. If they seize the seeds, obviously, you don't possess them.