Can i compose a multisig address where one of the signatories is a multisig address? Can i compose a multisig address where one of the signatories is a multisig address?
In order to create a multisig address we need the pubkey of the signatories.

bitcoin­cli addmultisigaddress 2 
'["pubkey1", "pubkey2",..."pubkey(n)"]'


Is anything stopping me from using a multisig address as one of the signatories?

Essentially: can one of the signatories be a multisig address (one that currently starts with a 3).
No this is not supported behavior. You can manually add the public keys from one multisig script into another, but a multisignature script can not be nested within another.