How to install Google Apps And Services on Lollipop AOSP ROM?
You don't install all the APKs individually. Since you've installed an AOSP ROM, what you are looking for is a gapps package that you flash in a similar way to how you flashed your ROM. You can get a minimal gapps package that will install everything you mentioned here.

You need not worry about converting them to system apps. When you flash the package from your recovery, they will be installed as system apps in the system parition.