You wouldn't think it would be so hard to write something that goes beyond book reports from wikipedia on the military forces, but I haven't seen much.
One decent article from Jane's notes how the Ukrainian navy and air force lost a lot of their forces in Crimea. Farley argues that the navy probably doesn't matter so much, which sounds right. What seems more disturbing is the large percentage of the Ukrainian navy personnel that defected to the Crimean/Russian side. That may indicate that the Ukrainian military isn't willing to fight if Russia attacks eastern Ukraine, and as important may be perceived by Russia as an indication that they won't face serious military opposition.
A broader Foreign Policy article discusses the (bad) shape of the Ukrainian military while not being too impressed with Russia. It concludes the window of opportunity for an invasion starts in early April (ground dry enough for off-road travel by tanks, experienced Russian military conscripts still in uniform) and ends in late May (experienced conscripts mustered out, Ukrainian elections legitimize the government).
The FP article makes sense as to what's the best window now - I still think the Russians would have thought the best window to attack was at the same time as when they went into Crimea, gaining surprise and with the Urkainian military fractured and political structure unstable. The fact that they didn't attack is therefore hopeful. OTOH, maybe they're just indecisive so far, and could change their minds.
One thing to note about the FP article is the April through May window degrades over the time period - conscripts are mustering out over time, the approach of May elections make it more obvious that Russia is trying to crush democracy, and Ukrainian military has more time to get its act together.
On what we in the West should do, Ian Brzezinski argues we should supply military aid and move up previously-scheduled joint military exercises in the Ukraine from this summer to ASAP. While sending ambiguous messages is sometimes helpful, I don't think it is in this case. If Russia invades Ukraine, we won't and shouldn't engage in direct military action to push them back - so we shouldn't have forces there in potential harm's way, not now and not this summer. OTOH, we can and should provide military assistance in case of invasion, and we can signal that to Russia now by providing military assistance now.
Cancelling summer exercises while initiating military aid should be a mixed message that isn't provocative while still confirming the cost side of the sheet as Russia considers its options.