1) not required but I highly recommend. I use these and they work well for karaoke https://smile.amazon.com/innopow-80-Channel-Microphone-Continuous-WM-333/dp/B0749L15PF

2) Bluetooth introduces a delay that makes it unusable for karaoke

3) OpenKJ is a great piece of software. I wouldn't invest in anything else unless there is an option you can't live without it doesn't have. However I recommend the Karafun subscription service and their software.

4) For a budget mixer I recommend these because they have vocal effects and XLR outputs

Yamaha MG06X

https://smile.amazon.com/Yamaha-MG06-6-Input-Compact-Stereo/dp/B00I2J4V5G

or Mackie ProFX6v3

https://smile.amazon.com/Mackie-ProFX-Mixer-Unpowered-6-channel/dp/B07XC3BHTL

For speakers I would recommend

Alto

https://smile.amazon.com/Alto-Professional-PA-System-TS310/dp/B07CKBWYV5

or Mackie

https://smile.amazon.com/Mackie-Thump12A-1300W-Powered-Loudspeaker/dp/B073V7MKQZ

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Finally I would recommend using the Karafun professional subscription service and their KJ software instead of OpenKJ. It's free to download and they have some free songs you can try it out with before subscribing. Their catalog is updated regularly so you don't have to worry about buying the latest releases. You can use your own external hard drive of songs in addition to their songs but I don't use my external hard drive much these days.