Regarding excerpts: we don't allow the same recording to be used in more than one project. So if you were to record part of this work for this collection, you'd need to record it again for your solo. It sounds like jumping through hoops, and in a way it is. We don't want the same recording in more than one project, so having someone do a fresh recording of it is kinda getting by on a technicality - following the letter of the law rather than the spirit.

I'd counsel that if you are thinking of recording it as a solo, don't bother with this collection for now. You could start recording it now with the intention of soloing it (you don't have to set it up as a solo in the forum right away; you could record first). If you decide NOT to finish it as a solo, then submit the excerpt audio here. But I don't think I'd record part of it and submit it here, then turn around and do the whole thing as a solo.
Does this make sense?
And yes - 30 minutes at a minimum. Preferably longer.
