Russia’s army has 280,000 personnel and its armed forces have 900,000 overall, according to the International Institute for Strategic Studies, with 190,000 in Ukraine. About 210,000 are in Ukraine’s armed forces. So Putin still has a significant force at his disposal.

Even so his next step will be to bring in foreign fighters, like the Syrians.

https://www.forbes.com/sites/alisondurkee/2022/03/10/does-russia-have-enough-troops-to-take-ukraine-heres-where-its-manpower-stands---and-why-its-recruiting-foreign-soldiers/?sh=7c97ad1d4d82

And China has certainly not said "no" to Putin's request for military aid.

Would Putin resort to using WMDs? I would not put it past him. Someone as insane as Putin might risk using those weapons. He has an enormous arsenal at his disposal, chemical, biological and nuclear.