Good luck with the endeavor.

A few comments if I may:

1) Go grab M's Miner Monitor (search the forum or google for mminermonitor).  Written by a member on the board, mdude77.  It can monitor both Antminers as well as SPTech machines.  In addition, one of the more important things, is the ability for it to send alerts and reboot miners based on definable triggers.  Here's a screenshot of what it looks like:


2) As you can see from the screenshot the S5's are fairly over-clockable.  I've gotten most to run very reliably at 387.5 (roughly 1250 GH/s), and some are rock stable at 412.5 (1350 GH/s).  If it runs for more than 3 days at a speed setting, chances are you'll be stable for a very long time at that speed.

3) As you might also see, there's 3 miners down currently, which is common with Antminers - they will blow up occasionally and you will need to replace them.  The original setup was 48 miners.  One fried immediately on powering up, the fan didn't spin up and it wasn't caught in time ... the burning smell alerted to something wrong, and that was it.  I've had 3 of them lose a whole chain (one out of the two boards, as you can see from the .128 machine which has errored out (gone down and needing a physical reboot).  Another one just keeps dying after being up for random amounts of time, so it's worthless.

I use breakout boards from Gekkoscience for the Dell 750 PSU's as well as the DPS-2000BB PSU's.  A single 750 will power an overclocked S5 perfectly fine.  A single 2000BB will easily power 3, and you can get them to power 4 if you have good cooling and stable power (208V though).  I am running 2 S5's per DPS-2000BB simply for cabling and organizational ease.  These boards are indestructable and quality made, I recommend them highly, and they're very accommodating for special orders as well as special cabling needs.

I would also look into the breakout boards from J4bberwock (look in the Marketplace -> Goods section or just search).  He has just come out with boards to run on an IBM 2800 PSU, which will allow you to safely run 5 S5's on a single PSU.

Personally, if I were you, I'd deploy both Antminers as well as SP-20's.  They take the same PSU/wiring setups so you can interchange the units and the PSU's without having to modify anything.  I don't have any SP-20's, but I am ordering an SP-35 unit because I'm curious about the build quality as well as the simple ease of just plugging it in and running, without having to do so much custom wiring.

Finally, for pool choice, with that large of a setup I'd recommend looking at running your own P2Pool node in-house if you can, or possibly contracting Kano or CKolivas to set up your own local pool node using their new pool software (CKPool) and hooking into their pool network (which is already over 6PH).  Mining on BTCGuild is nice, but you're losing quite a bit with the 2% fee at your potential size, and if you're doing as much number crunching to get started, you should take note of the pool and its fees (P2Pool has zero fee, CK has I think 0.9%).  I run my own local private P2Pool node behind a firewall and not exposed to the outside, along with another VM to run just the wallet.  I have been running a side-by-side comparison between P2Pool and BTCGuild and I can tell you from personal experience P2Pool has been getting better returns over the past 3-6 months, as long as you can live with the variance (sometimes 2-3 days between a block).

Feel free to PM if you'd like for more discussion.