Will music slow down my iphone 5 32gb?

I don't wanna know how much music it can hold. I just wanna know how much music I can put until the iphone starts being slow. If i have 8 gb of music will the phone be slow? You know what i mean?
I just don't want a slow phone

No, you will be fine if you only have 8GB of music on your phone. The phone shouldn't start acting slow until the is very little space left (300MB free is when mine started to get slow on my 4S) but 8GB will be fine, especially on the iPhone 5 which is a very fast phone in general.