1. Promotion above the expected level happens when there is a mismatch in the number of teams available the same level to make leagues - and usually happens at higher levels.

2. As above

3. yes, as above the max is 2,500 and that means no more people can buy tickets no matter what size your stadium. Here's the list:

L1 - 800
L2 - 2,500
L3 - 6,000
L4 - 11,500
L5 - 19,000
L6 - 28,000
L7 - 40,000
L8 - 53,500
L9 - 69,000
L10 - 86,500
L11 - 106,000
L12 - 127,500
L13 - 151,000
L14 - 176,500
L15 - 204,000
L16 onwards - 260,000

4. The youths are 18 yo (unless they arrive on Day 1 of the Season, then they are 19) iirc. As above is a free one and a Token one and the cost of signing the tolen one increases with his Quality rating.