Mac Pro 1.1 to 5.1 comprehensive upgrade advice?

I need some comprehensive advice on upgrade process, over the next 2-3 months, from my current Mac Pro 1.1 which is:

• Dual-Core 2.66 GHz
• 8 GB of 1033 ram
• 120 GB OWC Mercury Electra 3G SSD (boot and data)
• SSD backed up to internal 500 GB Hitachi Drive (CCC)
• SSD backed up to external 250GB FW800 Drive (CCC)
• Running Lion 10.7.5
• 2- 23” Cinema displays @ 1900x1200 res,
• Nvidia GeForce
  
  I’ve had this rig, give or take, for four+ years.

Main complaints:

• Slow Excel and Word updating and editing, Some charts take 5-10 seconds to appear or redraw, in spite of font fixes, 0 ‘recents’ setting, keeping a very clean ‘permissions’ set-up, and other good ‘housekeeping’.
• 7300GT PCI card starting to get a little "quirky" with occasional mangled screens
• Occasional ‘spinning ball’.
• McDraft slow to redraw.
• Generally, the 1.1 seems to be a bit too slow for me. I'm waiting on the computer, too much.
• Would like somethingh that has a bit more ‘pop’. I like for the computer to wait on me, rather than the other way around.
• Also, have not ruled out that I might be using some more ram and CPU-intensive apps in the future.

In looking at what’s out there used, and from what I read by the experienced folks here on the forum, I see the:

• 2010 or 2012 Mac Pro 5.1,
• 3.33GHz six-core,
• w/ 3-8GB Ram,
• 1 TB Drive
• 5870 PCI
• Moving up to ML or Mavericks.

as a very good ‘bang-for my-buck’ candidate. $2000+/-.

I intend upgrade the ram in the 5.1 to 24GB (3x8GB) @ $300., unless somebody talks me into higher, or another ram config.

Since my total usage for the last 3-4 years has remained fairly constant at 70-75GB, I intend to use:

• My existing 120GB SSD as a boot for the new 5.1
• Buy another 120GB SSD for a data drive
• use the 1 TB drive with 2 partitions, to back up the Boot and Docs SSDs,
• then do “belt and suspenders similar B/U with the existing Hitachi 500GB drive
• all with Carbon Copy Cloner, and bootable.
• Will be running one, possibly two, more 23” Cinema displays (or maybe a 23" and 27”)

User usage profile:

• Lots (50-60+) of heavily cross-linked Excel workbooks (many with ten to twenty 2000-3000 line, work sheets) with tons of complex charts, in 15-20 folders.
• A lot of long Word docs (100-150) pages, many of which subscribe to the Excel workbooks.
• Medium to large, complex, symbol library-rich drawings, in MacDraft
• Illustrator – light usage –simple stuff (amateur)
• Photoshop – light usage – simple stuff (amateur)
• Just getting into some GoPro Movie editing, nothing too big or complex. Vacation and recreation vids. (amateur)
• Some Garage Band stuff for my harps (amateur)
• Some 40-50 slide PowerPoint stuff, with more to come.
• Dragon Dictate, which is a bit sluggish on my 1.1.

Questions:

• Am I about on the right general track?
• And I’m ready to get something I can live with for another 4-5 years. Realistic?
• Ram upgrade to a minimum of 24GB -32GB? If so, Should I add 2x16 GB ram modules or 3x8 gig ram modules?
• Will be leaving some, but not too much, processing speed unused?
• What have I forgotten or gone astray with?
• Better/cheaper upgrade?
• Advice?

I know this is a long request, but I'm tying to make it in one concise and unfragmented attempt.