Capturing and storing website (SPA) activity in Marketo fields

Hi all

We'd like to record key dates and count of activity for our web-based tools and pages, and attribute to leads (ie add dates/counts to a field). Eg - we'd like to capture and record:

1. Date someone used a web tool (eg calculator) for the first time (eg recording click of button or visit to thank you page)
2. Count of times someone has used tool (eg calculator) - again potentially looking at button clicks or thank you page visits)
3. Date someone last used a web tool.

Many of these pages/tools exist within a single page application environment, so simple tracking of page views etc can be challenging. We think creating events via GTM and Google Analytics might be a solution. But not sure about if/how this data can then be pushed into a Marketo field.

Basically we want to 1) tell Sales when a lead of theirs has accessed one of our high value tools and 2) trigger promotional and welcome emails to leads based on whether they've used a tool or not (eg if use count = 0, send promo email. When use count = 1, send welcome email, etc)

More advance solutions might be required (outside of my skillset as you can probably tell), so looking for simple/quick win before we get the developers involved.

Any advice would be appreciated. Thanks.