Is there a way to get the same sort of behavior to aid with metering from an external flash? (in this case the Yongnuo YN560 IV)

No. The YN560 IV is a "manual only" flash. The preflash you are seeing when you use the camera's built in flash means the camera is set to use E-TTL flash that allows the camera to set the flash power automatically.

I've manually set the flash to its lowest setting and I took down exposure compensation to -5 on the camera (the minimum) and the pictures are still too bright. Is going full manual the only way option?

There's a lot to unpack here.

When you are using manual flash, the camera has no idea how bright the flash will be. So when metering it calculates exposure based on the ambient light and doesn't take into account anything about how much light the flash will add. So essentially, any amount of light from the flash will be more than the camera is expecting. If you are using any kind of automatic exposure mode with a manual flash, the camera will do everything it can to properly expose the shot without the help of any flash.

Going full manual exposure is probably the best option, because it gives you complete control over the camera. That is where you want to end up. How you calculate what flash power, ISO, aperture, and exposure time depends on how you're using the flash. Is it your primary illumination? A fill light in brighter ambient lighting? Something else?

But there are a few other things you can try:

• Move the flash further from the subject. The amount of light striking the subject will be reduced by the square of the amount you increase distance between the flash and the subject. If you double the distance, the light will be reduced by a factor of four, or two stops. If you increase the distance by 40%, so that the flash is 1.4X further from the subject than before, the light will be halved, which is one stop. Of course, this either requires you to also move the camera back or use a way to trigger the off-camera flash with a wired connection, radio trigger, or optical trigger in S1/S2 slave mode.
• Bounce the flash off the ceiling or a wall instead of pointing the flash directly at the subject. If the wall is a neutral color (white or grey) it shouldn't affect color too much, but if the bounce surface is not neutral, it will affect the color of the light from the flash that illuminates your subject.
• Reduce the camera's ISO setting. At high ISO it takes less light to overexpose than at low ISO. If you have Auto ISO selected, change the ISO setting to a manually selected value. You'll need to take most cameras out of "A" exposure mode and into at least "P" exposure mode to be able to manually select the ISO setting for many cameras.
• Stop down the lens' aperture. You can do this either in aperture priority exposure mode or in manual exposure mode.

These are not really good solutions, though. They're just quick fixes.

In the long term, you should probably begin reading David Hobby's excellent free tutorials at his Strobist blog. Lighting 101 is a good place to start there.