1. If a customer has 4 x SQL Server Standard (8 cores), does that mean I will also need to have 4 x SQL-SAL?

There’s no server + CAL model in SPLA.  You license either per core or per user depending on the product.  Remember, SAL is not licensed per server, but for each user that has access to that server.  Your question indicates you might believe a SAL is licensed per server which is not true.

2.  Is MSDN available through SPLA?  Is it through Azure?

MSDN is not available in SPLA, but you can license the individual components through SPLA.   If an end-user would like to bring their MSDN license over to your datacenter, you must dedicate the solution for your customer.  Yes, Amazon must play by the same rules.  Oddly enough, Azure (which is shared) does allow MSDN to be transferred over to their datacenter.

3. I received an audit notification.  Should I respond?

Yes. But don’t work on their time, work on yours.

4.  If I signed the SCA addendum, do I need to sign the new QMTH addendum?

Unless you are planning on hosting Windows 10 you do not need to sign the new addendum.

5.  If I buy from a CSP indirect partner, do I qualify for QMTH?

No.  Your company must be CSP 1 tier authorized in order to qualify.

Thanks  for reading,

SPLA Man