Paging Hugh Laurie.

Cuban Fury had to be largely re-shot after playing very badly with test audiences.

Russell T Davies wanted something he owned outright.

It would have made more sense for the Valeyard/Dream Lord to be the one who wants to travel back along the Doctor's timeline and destroy him, thus achieving 'peace at last'.

It was the PE teacher.

Skip the farting aliens, but the Dickens episode is great.

The number-of-regenerations thing could be written around lots of ways, but it is quite important to the character of the Doctor that he will, one day, die.

That's the problem with the Melody Pond = River Song reveal for me.  The
story needs the the emotional payoff of Amy & Rory getting their
baby back, but if that happens then it negates the big emotional impact
of what happens in 'Forest of the Dead'.  As the Doctor says: "Timelines
can be re-written." but River…