I need a computer just to open several internet windows simultaneously that play videos constantly. What specs should I look 4?

an i7 with at least 6 cores.

I'll just mention casually here that any video you allow to play in your presumed business must be properly licensed, so you might want to stick to videos of yourself.

any computer can do that.

what you NEED to do is to get a fast enough internet to support such a feat. depending on your videos' size, they may need 15Mbps per video.

Specsavers!

Any 7th gen or later i5 should do that without any issue. You don't need anything special. The newer i5's have more than enough power for that type of task. Intel has built video playing acceleration right into their newer chips.

One with a decent video card