Is this a business or home network? If a business, I recommend a dedicated server that is not a user's workstation. Workstations get rebooted, sleep, and are beholden to the user's will. A dedicated server can be left alone and just operate.
How much data are you working with? What file types are you using?
That being said, here are some thoughts on your questions. I am assuming this is a home or very small business solution.
1: Will installing OS X Server allow me to do what I want, or is there a simpler solution?
Yes, but you can also use personal file sharing which is on all Macs and does not require the purchase of OS X Server. If you are truly supporting a single client (assuming the other is also acting as the server) you will be server fine with personal file sharing. This is enabled in System Preferences > Sharing. But, I am a purist so I don't believe a workstation should act as a server. Some other options you might want to consider is the purchase of a dedicated server, a NAS device, or possibly a cloud solution such as DropBox. If you got the route of creating a server (off existing hardware, dedicated Mac server, or NAS) you remain at risk because you have not implemented a backup solution. The cloud sync offerings, especially for small data sets and teams, provides versioning and separation of data from physical location.
2: Can this be done wirelessly or do I need to run the server hard wired through the router?
For best performance, the server should be wired to your LAN. However, it "can" be done over wireless but you will experience issues overtime your wireless decides to go wonky.
3: Do both computers need to be running the same OS, for example, 10.10.5?
No. A "file server" can vend files to any device that can communicate with the file services protocol offered. OS X can offer SMB, AFP, WebDAV, and NFS. This allows for support of a wide range of OSes and OS versions.
4: After setting up the Mac Pro as the server are there any limitations or shortcomings that this creates when using the Mac Pro.
Using a workstation as a server can cause issues as mentioned above. Now, if you are the only "user" and you have multiple devices, then obviously you know when you are about to restart the server and can manage accordingly. Also, for server to be setup properly, you should configure additional services that are outside your focus. If you only plan to use File Sharing, then you can likely do fine without the other services.
5: Why do people talk about establishing a dedicated server on a hard drive or larger RAID enclosure, is that simply to provider access to a larger storage location, and faster transfer speeds in the case of a RAID setup?
All of these reasons and more. A dedicated server and dedicated storage adds resiliency and often flexibility to your deployment. Let's take a simple example of a Mac Pro used as a server. (I am assuming this is a canister Mac Pro not a tower). Assuming you maxed the unit out a 1 TB, you are looking at a device with no removable (or movable) storage. Should something go wrong with the host (the Mac Pro) your data is trapped inside the device. Depending on what Apple decides to replace, that data may not come back. So, having external storage (especially that is a RAID) means that if there is a problem with the host, the storage can be connected to something else and you continue to work. Now, a note about RAID. RAID is not backup. RAID is redundancy. Don't confuse the two and no matter what your solution don't forget to implement and TEST backup. Now, how is RAID good? If you are storing data on a RAID (mirror, 5, 6, etc) then you can lose a drive (or more) without losing data. This is critical. Drives fail. Entrusting all your data to a single drive is asking to lose data. Entrusting to 2 or more in a redundant configuration gives you a chance to recover from an independent failure. As mentioned, RAIDs also provide greater capacity. A single drive is topping out at about 8TB (12 TB if you have deep pockets). But a RAID can be 40 or more depending on the case and drive size. Just remember, larger data set, larger backup set. Plan accordingly.
Hope this helps get the thought process going. OS X Server is a capable product but if you are looking to solve a problem for one person with two machines, it may be a little too much. Sort of a swiss army knife when you really just need a pen knife.
Reid
Apple Consultants Network
Author - "El Capitan Server – Foundation Services"
Author - "El Capitan Server – Control & Collaboration"
Author - "El Capitan Server – Advanced Services"
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