Help with karaoke set up!

[JJLabrier]

Okay so I'm not an expert on amps and audio and stuff so I need some help!
I downloaded the karaoke app on my roku and bought a microphone, and so I thought all I had to do was plug the mic into the TV and I was good to go. Naturally I was wrong, and I need an amp for the mic.

The amp is on the way now, ordered 1 on amazon. The Lepai LP-2020A+ Tripath TA2020 Class-T Hi-Fi Audio Amplifier.
I plan on hooking them up to some old desktop speakers. Will they be good enough? Should I hook the amplifier to my TV somehow instead? I'm not looking for an amazing sound experience, as long as it's not too distorted and stuff, I'll be happy.

Next question is I heard that a mixer of some sort would be a good idea, so that the sound from the karaoke music and voice from the microphone mix and come out the same speakers. Is this true?

Any advice is welcome guys! I'm all ears!

Thanks in advance!