Hello,
SAP Note 1353266 - Additional information about MaxDB version upgrade to 7.8 will give you answer of all of your questions.
You can upgrade MAXDB for individual system as well but you need to check that whether all systems are using same software or not. If all systems are using same software then you need to upgrade the database for all systems.
As per PAM, Solman 7.1 cannot be installed on MAXDB 7.8.
Thanks
Sunny
