Use the following solution if you want to have less work further down the road (it is easier than it looks).
To really track everything you would want to track i highly recommend using Google Tag Manager (GTM). Installing GTM is not as easy as the integrated Google Analytics solution, but once you have done it, you will (almost) never have to touch code injection again.
If you have spent enough hours trying to get Google Analytics right in Squarespace you will love this. I used this guide to install GTM: Event Tracking On Squarespace Using Google Tag Manager.
And found this solution to track form submissions (still just a workaround, but really easy): How can I track form submissions with GTM?
Hope this help. For further questions feel free to ask here.