I've been using blogger as a cms for my website but then I moved to custom cms so do I need to add the Google Analytics Code again? If yes then how?
If the code is still in the header or footer you don't need to change it . Still , most of the time a CMS is changed is better to add the code again since it's a 5 minute task .
Probably yes, but first look in the files to see if the code is still there or not but if it is not then you do need to put Google Analytics tracking code again.
Once you have registered your website, you will get the tracking code. You can add it in your website and in case you happen to change your web design or something, then you can add that same tracking code again.
use a plugin for this purpose to add the code these plugins do not affect the page load of the website.