Hi Marcello.
From my point of view this is the best way. Chose one system for monitoring/maintenance (in your case the ERP, SolMan is an option) and connect the other systems.
I would see ATM as a must have as ASE is benefitting a lot on up-to-date statistics. But I would also set up the data collectors as they will offer you all the monitors available in DBA Cockpit.
Regarding resource consumption:
Data collection, ATM, planning calendar: they all run based on the job scheduler. So when you set up ATM on a JAVA system this will use some of the resources of that JAVA system's database. So no impact on your ERP.
Best Regards,
Jan