Is the afterlife timeless?

[Minyatur]

Are we without time in time/space?

No

Could we rest there a "billion years" between incarnation?

Yes

Could we access higher planes there where all our "dreams come true"?

You can perceive your current experience as already being the realization of your dreams.

Edit: pre-incarnational dreams and of a higher level as part of your free will.

I know eventually that would get boring.

Infinitely does and doesn't.

My desires are pretty specialized.

All desires are.

I want to experience for Creator what few others would want to experience.

That is the purpose of many-ness and humanity is no standard.

Is that a noble goal, to experience it for Creator?

It is.