For Marketo, you'll find more details in this Idea (marked Released) https://community.tableau.com/ideas/6133
For LinkedIn, I've come across a couple of posts on the topic but if you're interested in voting up the Idea check it out here https://community.tableau.com/ideas/9676
At #TC18 there was talk about a Dashboard Starter for LinkedIn Sales Navigator... Spotted at #TC18 Devs on Stage: Vector maps, a redesigned mobile app, parameter and set actions, and Sasquatch | Tableau…
The Google Ads connector came out with version 2019.1 I think. More details here Google Ads - Tableau
As you're looking for insights from folks that have used these types of connections in the past it would be worth checking out the WDC board ...
Hope this helps