Hi @future_vision ,
A couple of ways to do this that spring to mind, broadly....
You can either:
1. Push abandoned cart data into a Marketo Custom Object via API, then trigger an email(s) referencing this information. This means you are calculating the send logic in Marketo (ensuring they haven't purchased yet, etc)
2. Trigger a fully dynamic email in Marketo, pushing in the info at time of send - again via API.
Number 2 is probably preferred since then you don't need to keep the cart information updated in Marketo, which is tricky - particularly if you want an email series.
I would say best practice is to use a Customer Data Platform to log this activity via Google Tag Manager and then push the relevant info to Marketo, but that is complex. "Futureproofed" probably means something like this, since a CDP would be a core bit of architecture. Without that you can certainly do it, but it's integrating more systems I would assume.
Sorry, I'm unsure how this comes together with the products you have listed, but since most of them are analytics platforms, I think you will need more in the stack. GTM can certainly be part of it, but there are just so many ways to do this, realistically. What is your ecommerce solution?