While PT is the standard on the scoring stage its not for composing.
Digital Performer - Logic - Cubase are the main daws that composers are using.
Mixes are bounced to stems out of those daws and imported into PT for recording the orchestra and on to the mix stage.
My question to the original poster is - are you trying to mock full orchestra stuff?? or just needing some samples to go along with what you are tracking?
If you are trying to mock up full orchestra stuff for film/tv/multimedia your proposed system is slanted more towards higher quality tracking and misallocating resources in that direction. To mock up full orchestrations you need to head in a different direction.
To address your system specifically -
Gigastudio is not needed at this point. The libs you mention don't use it. Most libs don't anymore. Kontakt 2 is the current standard and most libs are using their own software. VSL now has its own player.
One Mac pro is not able to load a full orchestra template using the sample libraries you listed. You will need sample farm daws.
http://www.vi-control.net/forum/view...41de0ba9d4af34
This is the main forum for guys who are making a living scoring.
There are a couple other forums but those trend towards hobbiest although you may not get that at first due to the stong opinions they will offer. Once you hear there music you will realize this.
VSL's VI edition will require at least 4 farm computers. This is due to the the amount of ram each orchestra section will require. Even if you fully load your Macpro with ram (and thats a lot of money at the moment) your session loading times will be insane. Like 20 minutes to load that many samples. Then you get a crash and have to reboot ..... basically its not a workable solution unless you feel like pulling your hair out waiting for your computer to load.
Most guys are using one computer as their main daw. In my case I do not load any samples in this daw. This lets me change cues in seconds since the files load superfast.
Sample libraries are loaded in my farm daws. (currently shuttle pc's but moving to mac minis soon). With the sample farms I only need to load them once in the morning as I use the same templates for all cues. this takes time to develop but once you nail it its a thing of beauty.
Once I am working on a cue I will then load additional samples in my main daw Mac. Rather than change my big template I just add the new things in my main daw.
Symphonic choirs itself really could use 2 computers as a full load is around 3 gigs of ram. VSL can get going on 3 but there are guys who want a full up orchestra and they are using 5-8 farm pcs to achieve that.
You may want to not get the TC reverb as altiverb will give you everything you need plus it will recall with the session. Also the UAD card is probably redundant. the horsepower of a macpro will be far more than enough. The big ben is also overkill imho. The clock in the rosetta is certainly good enough. Take that money and buy some mac mini's.
The rosetta may not be the best interface for your purposes since you will need more inputs from the farm daws.
Do some research on the types of rigs guys are using at this point. We all would love to be able to work inside one computer but the libraries have gotten so damn good and HUGE that farm pc's are the only workable solution at this point in time.
Your choice of VSL is a good one. Will take more work in setting up a template and learning to mix it but it is capable of the most realism at this point. If you hate mixing than look at EWQLSO.
Symphonic choirs is unmatched so far. VSL has a choir coming next year but as of now EW owns the market.
Best of luck on setting up your system. Buy the big bottle of advil to go with the logic manual.!!
(logics a great daw - I'm just not smart enough to use it)