Requirements for a shop

Good morning,
I'm currently in the phase of gathering information about which shopsysterm is suitable for what I'm looking for. So the shop in Germany is not existing yet and this is a kind of a presales question. In case this is posted in a wrong section feel free to move it to the right place.

I will finally sell just 3 (three) articles therefore I definetely don't need an oversized shop, although it should of course contain the basis functionality of a modern shop - like payment, responsive design...and so on.
Each of my articles is described under a seperate domain with it's own joomla installation. This is caused by distribution issues, because the articles a completely different individual services and I don't want to concern customers. I know it's more efford to maintain different sites for each article, but this is not really a problem for me as I'm talking about just a few products.
Finally the user will be forward to the shopsystem (whatever it might be) in order to order the article online. One of those "articles" is kind of a service where a photo of the customer is modified in a very unique way and then printed completely individually on a very special surface. And this is my point now: during the order process the customer should be able to deliver a high resolution pic. Sounds easy, but it's obviously not as I already asked that question on other platforms - without a positive reply.
And a second question: I will present all three articles under separate domains each, but I will not maintain three shopsystems. Therefore it should be possible to handover from each domain directly to the section inside the one and only shop where the specidfied articel is sold. I think this is a standard, but I prefer definetely to ask even simple questions before being surpised after the fact.
Many thanks in advance in case you managed to end up at this line of my text and for any help!
Best regards and stay negative those times

Olli