Mac Pro 2010 triple boot (Snow Leopard + Windows + Yosemite)?

Question

Hello All,
This is my first question here, I'm usually trying to find the answer myself, but this time I wasn't able to find anything clear enough to me. So I hope that someone can give me clear and easy to understand answer. I must also tell that my English isn't perfect, but should be more than good enough for communication. :-)
I have Mac Pro 2010, 4 core CPU 3.2 GHz, 6 GB RAM, ATI 5870.
HD Bay 1: WD Black 1 TB - Boot Snow Leopard 10.6.8
(Just to add: I am happy because when I bought my Mac it came with 10.6. I am happy with it, it's stable, and I want to keep it as it is)
HD Bay 2: WD Black 1 TB - Boot Windows 7 x64 (bootcamp, full drive)
(I am very happy how it works, so I want to keep it as is)
HD Bay 3: WD Green 2 TB - for all kind of data storage
HD Bay 4: Was empty until yesterday, but now I have another WD Black 1 TB to put it in - still not formatted.
I would like to install Yosemite on that new drive (first I was thinking about Maverick, but then I saw that some new applications will not run, like Final Cut Pro X, new MS Office, still in beta, plus I would like to use iMessage, etc.), and keep everything else as it is now - absolutelly untouched.
• Is it safe to do it, or I can make some mistake and lose Snow Leo and/or Windows?
• Is position of the drives important? Should I, for example, put new drive in a Bay 3, and move data disk to Bay 4, or it doesn't matter?
• When I download it from App Store, and when installation starts automatically, do I have an option to select to keep untouched everything I have now?
(I don't want even to collect any data from Snow Leopard, like mail settings, bookmarks, applications installed - absolutely nothing, it should run as a totally new comp and without any interaction with Snow Leopard, except ordinary hard disk access, like any other hard drive)
• Will my bootcamp drive be safe, I will still be able to boot from it?
I was also thinking about this:
I saw that it is possible to make bootable USB flash drive with installation. If I do that, and if I phisically unplug all other drives except a new one, then do installation, shut it down, and plug back all other drives, will everything work? Will I have triple boot when I press option key during start-up? Does all this makes sense at all to you?
Finally, does anyone have some experience with Mac Pro 2010 + ATI 5870 with Yosemite? Is it smooth, no problems with graphics or some other things?
I will really appreciate some answer about all this.
Cheers!

Answer 1

Some tips about Yosemite and Core Storage from MacIntouch Reader Reports on Yosemite:
Ric Ford [MacInTouch]
Yosemite's changes have led to questions and confusion about disk formatting and partitioning issues, backward compatibility, and dual-booting Mac OS X 10.6 and Yosemite. Below are a few notes on these issues from an email discussion (questions, tips and clarifications are welcome). 
Core Storage changes debuted in OS X 10.7 Lion, with Apple's new FileVault 2 whole-disk encryption and hidden Recovery Partition.
Generally, running OS X 10.7 and up shouldn't corrupt or convert the HFS+ partitions used by pre-OS X 10.7 systems (still supported in later OS X versions). There are, however, a few special cases to beware, and this is where things get confusing. Here are some specific issues:
1) FileVault 2 encryption and "Fusion" drives both depend on Core Storage, so applying those to any partition will render it inaccessible by pre-OS X 10.7 systems.
2) Yosemite's installation process silently converts a partition to Core Storage, incompatible with Mac OS X 10.6 and earlier. Ars Technica's review describes this issue.
3) Running Disk Utility's "repair" function in Yosemite against a Mac OS X 10.6 (HFS+) partition has caused problems in some cases, such as making the Mac OS X 10.6 partition unbootable.
(A search for Core Storage on MacInTouch will turn up more discussion and tips.)
See also:
Core Storage [Wikipedia]
OS X Mountain Lion Core Technologies Overview (PDF) [Apple]
OS X 10.10 Yosemite: Installation [Ars Technica]
File system changes in Lion [Ars Technica]
Can't remove Core Storage from hard drive [Apple Discussions]
How To: Disable CoreStorage on Mac OS X 10.10 (Yosemite) [Symantec]
http://www.macintouch.com/readerreports/yosemite/index.html#d16apr2015