“Ukraine can hurt them badly enough to make Putin think twice.”
Sadly, not with the outdated equipment they possess. During the Gulf War, Iraq looked really good on paper, but the equipment they had was obsolete and we destroyed it like a hot knife through butter. The Russians will do the same to the Ukranians....it is their old stuff and they know how weak it is.
Also, I do not believe the training and morale of the Ukranians troops is good.
The Ukraine has only a few thousand actual soldiers of any quality. Otherwise they have a large group of interior police, border gaurds and conscript rabble. Their equipment is mostly trash, and much of what they have can't drive, fly, float or do anything other than make nice targets.
The Russian military is also somewhat of a paper tiger, but it's still much bigger than what the Ukraine has - and more importantly if an actual land battle broke out the Russians would have immediate air dominance and savage any large columns of Ukranian infantry or armor.
If invaded, the Ukranians would have to fight a guerrilla campaign and bleed the Russians till they left. Someone like Stalin would have crushed such a thing, Putin probably doesn't have the luxury of using those sorts of tactics in today's globalized world where pictures and video are almost impossible to stop.
If Russia pushes further into the Ukraine it would probably only be some of the eastern regions of the country. If they actually marched on Kiev, the Ukranians, given time, could make such an occupation very painful. That could be one of the worst mistakes Putin could make. The end result would most likely be devastating for Russia, and an absolute end to the dreams of recreating their empire.