Is the ZK810TST a true 4K projector?

It is a native 4K UHD DLP projector with a 3840x2160-class image and 2160p output. It accepts 24–85 Hz vertical scan rates.

How close must it sit to the screen?

With a 0.65–0.75:1 throw ratio, it throws roughly 0.65 to 0.75 feet of distance per foot of image width. A 100-inch wide image needs about 5.5 to 6.3 feet.

Does it need a lamp replacement?

No. The laser light source is rated for 30,000 hours, so there is no lamp to swap. That is its main advantage over lamp-based short-throw projectors.

Can it be mounted vertically?

Yes. It supports portrait projection, which suits tall signage and art installations. The 15 kg weight means you need a mount rated well above that.

What inputs does it have?

The listed input is HDBaseT, which carries video and control over a single Cat cable. There is a 3.5 mm audio output and a built-in speaker.

Is it good for a home theater?

It can work in a dedicated large room, but it is built for installs. It is heavy, has no wireless, and its short throw is aimed at fixed commercial mounting.