Jason,
Congrats on getting in position of setting up your own!
If you have team already in place, I doubt they cant set up moodle server as it's no different, or may be they havent got expertise in setting up web servers that's why you mentioned.
you can read about Hardware requirements here (updated upto Moodle 2.9, but wont be different for 3.0)
https://docs.moodle.org/29/en/Installing_Moodle#Hardware
and performance recommendations here
https://docs.moodle.org/29/en/Performance_recommendations
you read correctly here moodle requirements in terms of RAM is mentioned as 10-20 users per GB of RAM, but you havent mentioned an important word "concurrent". Just to explain a bit more, concurrent users means that many clicking something at the same time, so if you have 5000 users registered doesnt means you have to have 250GB of RAM installed, you have to do an estimate on how many max users will be using the moodle at one time and also their clicks depends upon many other things like for example taking quizzes puts more load on moodle server than just browsing through HTML pages or downloading a file.
you did mentioned setting up Windows server (and I read it with a smile), get Server 2012 R2, for the IIS v 8.5 coming with it is to date more reliable and performance tuned.
where you mentioned Dual core 2.0, mind you that is minimum requirement, if you are going for hardware already picking up from your existing, then look up for E3 class XEON, as E3 class have more clock speeds, where in higher class CPU (like E5 or E7) you will get more cores but their speeds are in bracket of 1.8 - 2.8. If you are buying new, then I'll recommend getting E5 xeon v3 with 6 cores - Hyper Threaded or wait for few weeks before E3 class v5 Xeon hit the market --- if you want to get specific CPU model, I can write that too.
Rest, try keeping database on a separate drive and it has to be SSD Drive, as database wont be that much in size that you have to get TeraByte drives. If you can afford RAID configuration, then that will be a plus. and which database to use? I have seen combo of IIS and SQL Server performing better (even free version of SQL Server - SQL Server Express edition), but MySQL or MariaDB doesnt perform any different, I have tested my windows based servers with MySQL and MariaDB and found MariaDB slightly faster than MySQL and is as well recommended by Moodle - rest what your tech team can handle easily should be database of choice.
Beauty of windows server is that you dont need any additional software, as IIS comes packed with everything. but you have to find a sweet spot for hardware that can perform.
you should add to your question, how many users will be using the Moodle, plus what type of activities are there? that will narrow down the approach for finding the best hardware.
Summing Up Hardware:
Try getting 3 seperate portions of server in terms of hard drives
1: O/S and SWAP File (ideally on SSD)
2: WWWROOT for Moodle and Moodle Data
3: Database Drive: again on SSD
Rest RAM and CPU type depends upon my query of how many users, and what they'd be doing
Software:
You dont need any things additional, except PHP will require Visual C++ libraries and depends upon which version of PHP you are installing, you'll find link to VC libraries besides. I tested mine with PHP 5.6 and 5.5 (both came with opcache bundled) and both worked perfectly.
Although 64-bit version of PHP is still experimental in these above PHP versions, but i ran them fine with no issues, you can download either of 32 or 64 bit.
Database : that remains your choice, if you are going with free DBMS's then MariaDB would be recommended over MySQL.
Web Server: That comes as a part of Windows Server O/S, but very importantly get Windows Server R2 with IIS 8.5. and no less (like Server 2012)