Hi Marko,
Glad you love it 
About tracking code - There are some tracking services already supported by Wix without getting into code, so search our help first (I believe this includes Google Adwords, Facebook Pixel, Google Analytics, and Yandex).
If you’re trying to paste code from a different provider - It really depends on what the code is doing, but typically these snippets will search for elements in the document, or otherwise try to access the HTML of the site. If you try to add these in your WixCode page code they will not work.
But… If the 3rd party has an REST API or other API accessible over HTTP, you could write your own JavaScript in Wix Code which listens to the relevant Wix Code events, and then forwards to the service provider using wix-fetch (the best way to send http requests from within your Wix Code).
Hope that helps,
Uval