How to get the shop up and running
Hi Hman
Well done for getting this far, it's a shame this is so neglected in Tiki. All that "advanced cart" and plugins for missing info stuff was dumped in tiki, as you say around v7, but was totally broken and mostly undocumented from the start, sadly our "wiki approach" to development sometimes is abused and i'm afraid this is one instance of that. We should really delete it all think...
I have a couple of shops running and the profiles (originally called TikiKart) were based on the first of those, but i haven't been able to tend to it over the years and others have modified it since, not always for the better imho.
I think (hope) i suggested to you that the built in payments and invoices system in Tiki was weird and also somewhat neglected and i use the PayPal "mini-cart" on my shopping tikis.
Sorry this is also pretty well undocumented but briefly: Add your account email to thePayPal ID (and currency) then add a {paypal} plugin something like:
{paypal' button_type="_cart" cart_action="add" item_name="The Thing" amount="42.99" item_number="item42" minicart="y"}
(sorry, no time to test, and i usually hook in the version minicart i need in the custom look and feel javascript pref)
Hope that helps, apologies for not having time to try and guide you in this direction earlier, we really need a developer with lots of time and motivation to clean all this up, but thanks for your interest, hopefully that will help eventually!