RAM capability--how much can you load? Limiting Factor?

I have a brand new iMac, 32 gigs of RAM, 3.5 i7 Quad Core Processor, and a 3 TB fusion drive and I’m running Cubase 7.5.10.

Currently, I have an orchestral template with 25 instances of Kontakt (each with 16 instruments) running and everything seems to be working great (the only issue is that it does take about 20 seconds for Cubase to save the file, including autosaves, but I think this is because I basically am doing an entire movie in one file with a whole orchestral score so there are just massive amounts of automations and stuff).

My question is really a theoretical one: what is the limiting factor in terms of how much I can load into a Cubase file? How many instruments?

In other words, could I load, say 100 instances of Kontakt? Now, I understand, if I were to try to play a note on each instrument of every instance of Kontakt, that would be a problem (I presume). Obviously. But, can I just load lots of stuff in, and as long as I’m not playing that much at one time, there won’t be a problem?

In other words, how is the RAM being used? Is it only when the notes are played, or is it also used to load stuff into the memory?

What is the limiting factor?

The reason I ask is because if I am, say, working on this movie score, yes I will have lots of orchestral stuff loaded in. But then I may have a cue which is totally different (non-orchestral) so I have to load in a totally different set of instruments in. At what point am i gonna bog down my system? Is it only when lots of stuff plays at once or is it also when lots of stuff is loaded in at once.

Thanks for your help in advance.

How much can be loaded at once is limited by your RAM.
How much can be played at once is limited by your processor and disk streaming (in case of sampled instruments).
If you are using Kontakt, there is a wonderful feature “purge samples”. It unloads all samples and then only loads those that are actually played. Useful when you have a 3GB KeySwitched string instrument only playing 5% of notes and articulations in your cue.

Purge works weirdly for me.

Lets say I have 12-14 kontakt instruments on a particular project. Cubase takes around 13 GB of ram .
When I purge EVERY kontakt instances, it unloads around 3 GB of ram, so Cubase is at 10 gb.

I did the test by closing Cubase and reload the same session ( with purged samples), and Cubase still loads around 10 GB.

I’ve the feeling that even if you unload samples, the kontakt patchs informations ( pan, volume , etc ) , FX, inserts, bus, automations, still take a huge amount of ram…

it can be a little more complex than just amount of RAM or processor. A lot is controlled on how you use kontakt. it is a DFD-reader for most people. The bottleneck when using vast amounts of disk reading can be the harddisk. of course with SSDś this is less a problem, but still…

a good explanation of this you can find here:
http://www.kontakttutorials.com/kontakt-tutorials/how-to-use-and-optimize-kontakt-dfd/

for the rest, when using large setups, everything is about having a good balance trough the entire system.
if it is working fine, i would say do not change things untill you have a problem
i have seen people crippling their system just by tweaking around without a proper need to do it.

but if i have to choose a bottleneck in your system: no doubt i vote for the audio driver who will not be able to keep up when playing vast amounts of tracks at the same time, and processor as a second guess

added to reply to the question:
the number of intrument tracks in cubase is technically unlimited.
the number of instrument slots is limited to 64
http://www.google.be/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CD0QFjAB&url=http%3A%2F%2Fwww.steinberg.net%2Ffileadmin%2Ffiles%2FPRODUCTS%2FCubase%2FGeneration_7%2FCubase_7%2FDownloads%2FCubase_Comparison_Chart.pdf&ei=5kMrU7SjEMK47Ab16oCwBw&usg=AFQjCNECHlby4Yi01qhUPgdXeXDP0ne-KQ&bvm=bv.63316862,bs.1,d.bGE

kind regards,
R.