Russia used CW in Syria and here in the UK, and what was the response from NATO? Nilch. If they were going to use dubious weapons, they'll start there.
The fact that they haven't used such weapons yet suggests that Russia are in fact conerned about how it may escalate, regardless of the above response.
With Nukes, like you mention, how would it benefit them? The risk of esculation from NATO simply doesn't marry up with what little they'd gain from it.
I've said it a lot, but I genuinely think the chance of a tactical weapon is very slim and would only occur after they'd used other weapons.
Does this include wives?