It's a bold move but I don't see it changing the outcome of the ongoing war. If Ukraine could build long-range ballistic missiles in the near future, I think they could regain the advantage even without any nuclear warheads. Nuclear warheads would not be useful without those ballistic missiles.
A nuke seems like overkill. You would end up wiping out the population of Climea. If people didn't die in the initial blast they would certainly die from the nuclear fallout in the coming weeks, months and years.
Just use a powerful traditional explosive. You could even blow up a gas truck.
Man fuck these comments, nuke Russia you pussies. I'll deliver the missiles myself if that's what you need. Strap me to the rocket and fire me at Moscow!
Nuclear bombs aren't something you throw together in a afternoon. Also they primarily impact civilians. Precision is what they need. Take out critical components.
While I agree with your second argument that Russia would probably just call them on their bluff, I don't think they'd need long range ballistic missiles. They seem to operate on russian soil a lot, and you could put a big nuke into a larger van easily.
Just package it as a good old gravity bomb or glide bomb?
Or get creative and mount it on a swarm of large drones (with the others being decoys for SAMs). Maybe like a fleet of old prop planes flying very low.
This is very hypothetical though, no one should hope for Ukraine reaching the point of even considering an actual launch of a nuke.
Better to focus on targeted attacks. I think the Ukrainians know there country so guerrilla warfare is a better idea. Keep the Russians miserable and fearful of surprise attack. Ukraine can't beat Russia but they can break the spirit of the Russians so that they end up going home after years of embarrassment.
I think it isn't all that different then Vietnam or the US revolutionary war. Both victories were people who were protecting there homes. They used local knowledge and clever tactics. If the Ukrainians can keep the sky clear and stay hidden they are good.