GST Invoice query....

Alphanumeric is not compilation

1. Consecutive means suppose Series R001 is started it goes R001, R002 , R003 , likewise after R003 you cannot issue R009 mean cannot skip/break series . Yes you can start different Series like G001 onwards.

2. No Alphanumeric character is not Mandatory. Yes you can use only Numbers Yes you can use special characters. (Ref. rule 46(b))

Multiple series of invoice is allowed in same GST registeration?

Yes multiple series in same registration allowed.

Yes it is allowed.