Complete newbie here, as there are many Linux and Asterisk GUI’s out there, does anyone have an opinion on whether or how much they would degrade the server performance and if they would make my life easier (as being a windows developer tasked with taking over our asterisk systems)?
Have a look at FreePBX.
They will mainly effect the performance of call setup, whereas the bottlenecks will be with media handling.
As with any GUI, you will be largely limited to doing the things the GUI developers want you to do and won’t get hte full capability of Asterisk.
They will use terms that are not used in the general Asterisk community and they will be difficult to support by the general Asterisk community.