99999
15 of them.
27
6
More than one
Possible solutions - using your rules are:- 11,13,17,31,33,37,71,73 &77
There are 60480 numbers.
There are 4^6 = 4096 such numbers.
8.
If the digits are all different then 18. Otherwise, 192.
15 of them.
27
6
48 of them if digits may not be repeated. 100 if they can.
More than one
Possible solutions - using your rules are:- 11,13,17,31,33,37,71,73 &77
There are 2000 such numbers.
If you don't repeat, 20. If you do, 58.