No running 5 instruments in 5 instances only uses marginally more resources than 5 instruments in 1 instance. And even then it’s not straightforward (but we’re drifting towards the deep…). What consumes the bulk of the resources are the number and complexity of the instruments, not how they are grouped together. If you start to get close to running out of resources (you probably won’t with ARIA) do a Render in Place to create an Audio Track from the VSTi & then disable the Instrument Track(s). Also once you’ve loaded and configured an instrument in ARIA (or any VSTi), you can close its Window which doesn’t need to be open to play.
How many Tracks do you anticipate using?
FYI we encourage folks to put their system specs in their signature. Makes it easier to offer advice knowing what folks are using.