Odoo Studio is intended for expert users, not developers.  It can also be a good tool for prototyping.  An experienced developer can probably make the same changes more quickly without Studio. 

It should not affect system performance (it doesn't create Python code).

You will lose any changes if you uninstall Studio (it will show you what will be removed before you confirm to uninstall).   

Yes, you should be able to download a database from odoo.sh and move it to a local instance, but you need to have the same version of Odoo.