Yes, David Tennant did appear in the 50th anniversary episode of Doctor Who, called The Day of the Doctor.
I don't think so. After the human version of the doctor went with Rose Tyler to the parallel universe, they don't appear again in the program. Both actors (David Tennant and Billie Piper) do appear in later series (in the 50-year anniversary), but not in this specific role.
The weeping angels appeared in the doctor who episode Blink episode 10 of series 3 doctor who
No.
The Time Warrior.
no, but torchwood will cross over with doctor who
Essentially, in the episode of series 4 'Turn left' He was behind all the events that occurred but did not appear during the episode. Therefore he, in a sense, already has but whether or not he will return and appear in an episode we are not able to tell.
He was in two episodes. He joined the Doctor and Rose at the end of the episode Dalek and was taken home and left their in the next episode The Long Game.
Sarah Jane Smith first appeared in the Doctor Who episode "The Time Warrior" in 1973.
The comedian Ken Dodd appeared in the Doctor Who episode Delta and the Bannermen. This episode first aired from the 2nd of November 1987. Ken Dodd played the role of the Tollmaster.
Presuming you mean David Tennant, there isn't a set date. But in the 2009 specials of Doctor Who, David Tennant will appear in all of them so therefore the last shall be his regeneration. It is assumed that December is the most likely time. Possibly Christmas Day. Possibly New Year's Day. Or maybe even in January. So winter is the only definite answer I can give.
The Kandyman (proper spelling) in the 1988 story The Happiness Patrol.
The Eleventh Hour.