Is it possible?

to me an astral plane is much like an alternate dimension. so I guess if you create alot of astral planes you have your dimensions just put doors and halls and such in it. and personally I would say do it whenever.

To create a alternate dimension, ahh the glory days. Yes I believe it's possible, as there probably is those things anyways.

With multiple doorways? I'm sure theres a couple that have doors leading to their kitchen or pantry. But the world? Define the world first and I'll get back to you on that one.

i think it is possible to make another realm with enough strength (magically) and mind power. and as for the doors to get into the realm, i could be a ring to even a hole house for that matter that we could make to get into it. but if the gateway (portal [doorway] ) is not built right we might not be able to get through to the other side.