Nope. Independent Regiments can do what they want down to the lance level. See: FM: SLDF
Nope. Independent Regiments have 2 ASFs per company. 2*9=18
Yes, see Era Report: 2750 page 110.
The Star League Defense Force used homogeneous companies and battalions of Battlemechs and armor. If players with to have a more Star League feel to their SLDF units, instead of rolling on the Unit Composition Table for 'Mech and vehicle mass they may roll 1d6 for the mass of the entire lance.
Then we have FM: SLDF that says on page 14, "Standard SLDF doctrine to combine 'Mech types in units not smaller than a company. This simplifies both unit logistics and company training methods, and encourages MechWarriors to think of themselves as part of their parent battalions and regiments. Exceptions are sometimes made--most often in independent regiments--for graduates of the Gunslinger Program, and for 'Mech companies assigned to SAS units.
From that passage alone it's rare for all but SAS units to have mixed units in their structure. So if you have a line unit it must adhere to a single mech type per company. A Light Horse regiment, for example, can have Wasps in one company or battalion and all must be the same type.
It appears that they changed the ASF assets from the earlier 1 squadron per battalion. It's an improvement.