Moving Mavericks around. Good idea? Or not?

You cannot clone just the operating system and leave all the other stuff behind. But you can clone OS X from another computer then restore the clone on a different computer provided the version of OS X being cloned is compatible on the target computer.

Bear in mind that when you do this you also get the same system and user preferences of the source computer. You will need an external drive as the intermediary or connect the two computers using either a Firewire or Thunderbolt cable and boot the target computer into Target Disk Mode.

Clone Yosemite, Mavericks, Lion/Mountain Lion using Restore Option of Disk Utility

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

1. Select Disk Utility from the main menu then press the Continue

button.

2. Select the destination volume from the left side list.

3. Click on the Restore tab in the DU main window.

4. Select the destination volume from the left side list and drag it

to the Destination entry field.

5. Select the source volume from the left side list and drag it to

the Source entry field.

6. Double-check you got it right, then click on the Restore button.

Destination means the target computer's hard drive. Source means the internal startup drive of the source computer.

If you use an intermediary external drive, then you must first boot the target computer from the Recovery HD on the external drive so you can restore the clone from the external drive.

You really should not copy one working OS from one Mac model onto a completely different Mac model. There are drivers that may be specific to that model installed into the OS.

A mini can be cloned to a similar model Mac mini, however you need to think about things like iTunes authorisations (de-authorise it before you begin), and software licences. If you clone a Mac some software will just stop working if it sees a duplicate licences on the network or it may require you de(re)register copies on their servers.

You could boot one mini in 'Target disk mode' & connect it to the other Mini, from that point you can clone one disk to the other.

How to use and troubleshoot FireWire target disk mode - Apple Support

Take a full backup first (of both mini's incase you make a terrible mistake 🙂). Disk Utility can clone disks, as can Carbon Copy Cloner.

You also seem to want to merge OS's (if my understanding is correct). Whilst this is 'doable' however it is a terrible idea unless you have lots of experience & understand the OS. Again merging from one model to another across OS versions is not advisable. Why can't you just install the software you need onto the desired Mac?

You seem to be mixing up 10.8.5 & Snow Leopard (10.6) too, a 10.6 DVD can't be used to install 10.8. I assume you mean you installed 10.6, then downloaded 10.8 to upgrade the OS?

Frankly I consider it misguided to want to upgrade any Mac when it is working well & it is known that the next OS does not support the required software. What exactly do you gain by going to 10.10? Can you dedicate one Mac only to the things you need on 10.10?

I would agree with Drew's last remarks. If you have mission critical software, then never upgrade until you know your software will work on the upgraded machine.

See App Compatibility Table - RoaringApps.

This may or may not work. Download the OS X Recovery Disk Assistant along with a 4GB thumb drive and run it from your Mac Pro that has OS X Mavericks.

The utility will create a Recovery HD of the version of OS X you have installed (in your case Mavericks) onto the thumb drive. Then unplug it from the Mac Pro and restart your 2011 Mac Mini using the Option key and select the thumb drive. This will take you into the OS X Utilities menu. See if OS X Mavericks will install for you (Reinstall OS X - selection).

On the Mac Mini 2012, go to the App Store Purchases tab and see if Mavericks is there. If so, download it. You can then transfer the installer to the other computer or make a bootable USB disk using this free program.

Bootable USB Flash Drive – Diskmaker X