AFAIK The Chechens were ex soviet military and had been operating a large scale black market for weapons - so they had plenty on hand. Towards the end of that conflict Russia started using AA guns on the tanks to counter the ambushes. I’m pretty sure they learned a lot from that experience.
They were, but a lot of Ukrainians have military service experience. It also seems like Russia didn’t learn those lessons, and others. Their armor looks to be stretched thin. In urban fighting having lots of people firing from a lot of places on advancing Russians will make it hard for them to focus air support. Just pinning down small groups of Russian infantry will allow the Ukrainian army to roll them up if they can maintain mobility.
