Well... paypal is secure for that kind of stuff....
BUT...
There really isn't a lot of money in doing that Darwin, unless you have a bulk-buying capability, and even then you'd probably invest more man hours than it is worth to get money back from them... especially if you include a screen. I don't mean to shoot you down... but I have seen 3 people with your idea go in to debt and they're still working it off to pay for the systems they made and sold. (they had a profit on each one, but the profit was less than if they had a real job and thus they did not support themselfes well enougg to survive.)
Ahh well... it's up to you. Good luck!
(I would not know where to get such a license. I would just keep track of all of the product reciepts from the parts you buy, and the systems you sell, and then when taxes come around, add the difference in to your salary I guess? I actually forget how you write in profits like that. oh well.)