Most Agave are monocarpic - they flower once and die. Sometimes offsets are available from the dying plant. What you have in the picture is the flowering stem.

Q1-yes, as long as it has porous root run

Q2 - 14-19 years in nature, perhaps more or less in cultivation

You wouldn't need a giant container for a long time. This is very slow growing and ones in commerce are generally not very large. Flowering is irregular and only on mature plantings (10 yrs+ ?).......not sure how likely these are to flower in a container setting and not sure you want it to anyway. LIke other agaves, it is monocarpic (dies after flowering) and this species also does not produce pups or offsets.

@gardengal48 So this might make an interesting species to grow on a slope where they could propagate and cover the slope over time.

@cactusmcharris Will the root run long and deep?

The 'harder' you grow agaves the less likely that they are to bloom. So poor soil and little water retard blooming, the reverse accelerates it. So to some extent you can push it one way or the other.

I thought they don't mind some shade either

Many Agave species are native to open pine/oak forests at higher altitudes in the mountains of Mexico, where they receive partial shade from the trees and have slightly cooler temperatures because of the higher altitudes. Most species need considerable shade in the hottest low desert locations like Phoenix AZ, except for a few species that are native to very hot low desert areas. A. deserti is one.

A. montana is native to northeastern Mexico at altitudes up to 9,000 feet, making it fairly cold hardy (as Agaves go). A. montana is solitary in habitat. In cultivation, some solitary Agaves will produce an offset or two. A. parryi truncata is good on a slope, because it offsets away from the original plant, instead of creating a wadded up clump all muddled tightly together. It's also a rather flat, low grower, a good form on a slope.

Does anyone know of a source for two large-specimen Agave Montana in the US? I am in California but I can mail order them. I noticed quite a few of these are showing up in the UK, so they must have a big propagator there.

Is there a reference that shows all of the varieties of Agave Montana? I understand that "Baccarat" is one of them.

https://www.google.com/search?q=agave+montana&client=safari&rls=en&source=lnms&tbm=shop&sa=X&ved=2ahUKEwjmjOyO1IbrAhWGs54KHcrQD2cQ_AUoAXoECA4QAw&biw=1352&bih=848