Questions about Sigma 24-70mm F2.8 DG OS HSM ART, Canon EF

Should already work. But that results in a 38-112 mm lens because of the cropfactor of 1.6. Wouldn't make sense for me.

Yes, because the 80D has an EF-S bayonet. This lens has an EGF bayonet and is therefore compatible with the EF bayonet of the professional line as well as with the EF-S bayonet. It should not be forgotten that the smaller sensor brings a crop factor with it, the 24-70mm of the lens becomes approx. 36-110mm on an 80D.

The lens is compatible with the EF to R bayonet adapter, without this it is not possible to attach the lens to the EOS R

Yes this lens fits the Canon 700d mentioned. :)

I think so. I just bought it here 2 weeks ago. Selling a house is always more expensive, and in Germany you might pay even more VAT. All information without guarantee, but according to the designation clearly the newest. It's a great lens and I can recommend it!