Huggett offers 2 alternative interpretations of T-duality, in connection with the 3rd question. Two interpretive decisions need to be made:
- First interpretive decision: either the T-duals agree on the physical world, or they do not. If they do . . .
- Second interpretive decision: do both say that strings literally live in a space of radius R (but represent that fact dierently); or do they represent facts the same way, and so say nothing beyond their shared consequences (so that the radius is indeterminate between R and 1=R.)
Either way, both interpretations agree that the target space’s radius (i.e., the phenomenal space we live in) is very very big. Whew!
Beyond Spacetime 
Disagree with that! There are three interpretations here – first the duals could disagree, then there are two ways for them to agree. On the first, target space is phenomenal space; on the second, target space has indeterminate radius and so cannot be phenomenal space, since that does have determinate radius. (So what I think I’m disagreeing with is the claim that target space is always big – what I said is that phenomenal space is big. The point being to drive a wedge between them.)