Re: the mini-offensive in the north, what about the Russian separatist outfits that did some attacks near the border toward Belgarod. Rather than have to move Ukrainian troops from other areas, ask those hungry chaps to assist at that front.
I think they tried doing that when they had to at the very beginning of the war. I don't think it worked out that well.
I would doubt that a Russian separatist unit mixing along a front would work out well. They would fairly undisciplined troops mixing in a chain of command that would be more disciplined.
For one their commanders are not very accustom to being in a large staff chain of command. And none of their commanders would be mixed in with the staff officers. So they would not feel at part of it.
There's also the problem that they are Russians, and at this point Ukrainian troops hate Russians.