Question on Teachers - okay Transfiguration teachers in particular

[karenlyall666]

No: HPFGUIDX 69199

Does anyone know of any canon to back up the theory that there is 
more than one teacher per subject at Hogwarts?

I ask as I need some input for a personal project...  The fact as I 
understand them are - 

1 - C1940's AD is Transfiguration teacher.
2 - At some point after this he becomes Headmaster (thereby giving up 
his 'day job' as teacher).
3 - 39 yrs ago (1954)  McGonagall becomes Transfiguration teacher.
4 - 36/37 yrs ago (taking Snapes age from the JKR interview as 35/36 
in the previous book) Remus Lupin is born.
5 - POA, Remus states he could only come to HW as AD was Headmaster 
(I always took this to mean AD had got the job not long before RL 
turned 11). 

Here come the questions -

Who was Head before AD?
If fact 5 is correct what was AD doing during the intervening 15 yrs 
(1954 - 1969).
When was AD offered the MoM job? (The Quibbler article states Fudge 
was given the job in 1990 - is this when AD was offered it?)

as a side note...  

How did Fudge manage to get from Jr Wizard in the Ministry to 
Minister for Magic in 9 short years?  Looks like there's still hope 
for Percy 'Minister of Magic wannabe' Weasley!!

Any help grately (oops! obviously concentrating on how great Floo 
powder would be) appreciated.

Karen