Manual Testing/Automation - Selenium webdriver/TestNG/Nightwatch.js

I am still new to automation, I've created a few tests using webdriver and TestNG - Data driven passing in parameters from Excel etc.

I am in a manual position so mostly doing manual Test Plans etc.I am Self taught selenium, webdriver etc. I am still basic using Java and just starting to understand everything. I've managed to create tests filling out forms on webpages and checking if they were submitted etc. How much more advanced do the UI automation tests get? Also what else do automation testers test apart from web/software screens?

Also I want to move into automation full time as I cant see a long serving career in manual test plans, Would I be out of my depth instantly joining an automation team with only being self taught and only having basic java language skills?

I use selenium Webdriver + java bindings + TestNG framework with data driven approach, If I was to use nightwatch.js and script my tests in java-script would I have much difficulty converting from java to java-script?