Serbia is theoretically neutral but practically somewhat Russia-aligned, so some Serbian people I know have been giving me information there.
Estimated Ukrainian military losses are pretty small, actually. Their materiel isn't being captured. They lose troops mostly to shelling, and Russia is sort of just shelling at random, they don't have good intelligence on potential strongpoints (which is why doofuses posting their location on social media and Russia bombing the fuck out of them is such a common theme right now, it's literally the best intel Russia can get).
And while Ukraine's economy is hurting on small arms, they have two refurb programs ongoing for updating captured mounted machine guns into practical man-portable shoulder-fired units, they have taken a page out of the Kurdish resistance book and begun putting together cheap anti-materiel rifles to match them, and they have at least Germany providing SUBSTANTIAL arms assistance, including the PzF3s they donated most recently (which even the latest Russian tanks should be total kills with).
One problem I see continuing to come up with Russia's approach is that they have no combined arms doctrine worth mentioning. Their tanks are in all-armor units, making them easy kills for sneaky mechanized infantry. Their infantry are not well-organized either, it seems.
I can't speak to the hypersonic missiles with confidence, Cain might be able to. I can say there are two LIKELY scenarios:
1: Putin waving his dick.
2: Pattern of escalation. "We don't want to do this but you give us no choice." The T-14s rolling out en masse to get totally fucking crushed by Ukrainian anti-armor units should be next if that's the case, and after that we might be in danger territory for actual nukes -- probably tactical payloads on theater ballistic missiles to start with. I think Russia would deploy any potential "Wunderwaffen" they have before that point. It's a really WW2 playbook Putin's using as a general rule, so I am not ruling out Russia having some under-baked top mega secret weapons programs they think they can deploy before the big guns come out.