for the js you just need to add you js into master.blade.php
I got your question please have a look of that doc
I got your question exactly the velocity is a package which contains all the css and js and all functionality for the velocity theme,
But if you want to develop a package in bagisto for default and velocity theme then you need to do compatible to your package for the velocity theme.
Let me know if you still got some questions.
Basically Controller is work for a route, so if you are want any specific route should be called using your controller then create a route file in your package & used same name of route as it have in core & when this route hit, call your controllers method.
I got your issue , in the address1 is the exploded array string
if you visit in the directory
then you can see. and if you want to customise any data then simply you can do.
you should send your data as array type separated by 
like if you want to send multiple customer name then simply send
customer_name = 'name' customer_name = 'name2'
if you still found issue let me know,
Can you please explain me your issue ?
if you want to update library simply run composer update,
if you still found some issue let me know.