If Russia did not have nukes would N.A.T.O. have opposed Ukraine's invasion sooner, more aggressively and directly?

Nope.

NATO is really only obliged to defend NATO members and since Ukraine is not one, I doubt they would’ve done much in either case.

The fact is that even without the nuclear question, people in the West would not have supportive of getting involved in another war.

NATO would have quickly established a no fly zone over Ukraine had this not required attacking radar sites and surface to air missile bases on Russian territory and risking all-out war with Russia.

No.

I don’t think it’s a matter for NATO per se. The US, however, is a different matter. They have a long history of piling into other countries’ wars, especially if Russia or China is involved. If not for the prospect of nuclear war I think the Americans would have counter-invaded Ukraine very early on. They may still do, but it wouldn’t be as NATO. Russia’s war would be with the USA, as no NATO member is under any obligation to become directly involved. America doesn’t give a toss about Ukraine, but it does about Russia, and that’s what this is all about. The irony is, Kennedy threatened the world with nuclear war over Soviet missiles in Cuba. Now they’re expanding their military empire right up to Russia’s borders, and wonder why the Russians don’t like it.