First for good info for rooting your phone check xda forums. They surely have a forum for ur phone and surely have someone who rooted it and has more experience and is willing to help out.
For a store u could use apkpure app store (no account needed) or apk mirror
Be careful when rooting because there are risks of bricking and such. Dont root ur main phone it might be risky since its ur first time.
I personally use AIMP. It has a built in converter it worked well for me