I'm fairly new to playing guitar, I have an Alvarez rd210 acoustic which came with elixir strings. I'm not sure which gauge they are. The coating is coming off all the strings I want to replace all the strings and was going to put plain strings on. I thought there was a standard, but i see light, extra-light, medium. I'm not sure what size to get or even what's on there. I'm not even sure what is a good brand to get. Thanks for the help!!!!