White_Magic

No problem man. I am not sure about the adapter limiting the speed, I would think not. I use a TB to Ethernet adapter from my MacBook Pro to share the wireless connection to my Mac Pro and I have no problems with it, but then again the speeds are nowhere near 300MB/s+. I don't think there should be any issue though.

I use the Astro A50's. I know Linus didnt think that highly of them, but I really enjoy them, but they did crap out on my after 6 months of daily use. But I had a third party warranty(first one i ever bought actually) and they replaced them and reset the warranty time to extend it from 2 years from the day I got the replacement. Other than that, the battery life is really good if you remember to charge them when you get done. I dont really have much experience on PC headphones, I bought the A50's for my XBOX One and they are the XB1 version, but I have them running through the Optical Audio form my MacPro. What is your budget?

In the App Store download the OS X version. Problem is you can only download an version to update your current OS X or a version you previously downloaded. Run the OS X Installer.app. Its nice to make a copy of this installer.app because it will be deleted from your iMac harddrive once the install is complete. Anyway, run the installer while the external drive is connected and mounted. Go into Disk Utility and format it to GPT to ensure the format is correct for OS X and so it has the name you want. The installer will ask you what drive you want to install that version of OS X onto, select the external drive and you should be good to go. Just follow the onscreen steps. I have done this many, many times. I have a MacBook, MacBook Pro, and MacPro. I have installed and ran OS X on many external drives and even had my MacBook Pro running on OS X 10.11 El Cap from an SD card. Any questions feel free to ask. I can get you more detailed info if you need. All I use is Mac. EDIT: I agree with what others have said, try to get an adapter for USB 3.0 to Thunderbolt if possible. TB hard drives are way too expensive. I recommend using a 2.5" external hard drive carriage that has USB 3.0 connectivity. It is what I use for external SSDs. I run virtual machines and even OS X natively and get R/W's of 300MB/s. Which is not bad for an external SSD through USB. More than adequate considering the speeds of mechanical hard drives. Another option would be to make a Time Machine back up, install the SSD(if its easy to do on your model iMac), then boot into Recovery using CMD+R as soon as you hear the boot chime. You should be able to do a network recovery which will download and reinstall OS X onto the SSD. What year is the iMac? If the iMac is too old then you wont be able to do a Network Recovery, but judging by the hardware you should be good. Once you get to the Set Up option screens for OS X you should see the option to "Restore from Time Machine Back Up". Time Machine back-ups literally make your machine the EXACT way it was when the back up was made. Literally EVERYTHING is the same. Only thing you have to do is redo your passwords for iCloud or the Mail app and things like that. SECOND EDIT: Just like you would boot into Recovery by holding a key combo after the start up chime, You can choose the exact drive you want to boot from by holding down the Option/Alt key right after you hear the boot chime. This is how you select the drive you want to boot from, whether internal or external. It may take a little while for a drive to show up, especially if it external, but if you feel like it takes too long or doesnt show up then unplug then plug it back in. It should show up fairly quickly after that. But you can definitely boot from any drive using this. I am currently triple booted with my Mac Pro. This is the Mac equivalent of going into BIOS and selecting boot order. Thunderbolt to USB3.0/eSTA http://www.amazon.com/Kanex-KTU10-Thunderbolt-eSATA-Adapter/dp/B00LOLBBQQ External HDD Case for 2.5" drives http://www.amazon.com/Sabrent-Tool-free-Enclosure-Optimized-EC-UASP/dp/B00OJ3UJ2S/ref=sr_1_1?s=electronics&ie=UTF8&qid=1459726820&sr=1-1&keywords=ssd+external+case

OS X 10.10.5 on my MacPro, OS X 10.11.3 on my MacBOOK Pro, Windows 10 for BootCamp on my Mac Pro, and the random Linux distro I feel like using at the time either natively or as a VM

I had a "Full Install" DVD of Windows 8.1 lying around my house. Right when Window 10 came out I tried using the WIn8 DVD to install it on a laptop I bought from a company(end of life equipment they would normally throw away). It said it has been used to activate too many machines already, I do not know how many times it was used to activate Win8 as this DVD and Activation Key were something my father used on his computers. In November of 2015 Microsoft updated Windows 10 to allow us to activate a "clean" install of Windows 10 by entering a valid Win7/Win8 key, which means we dont have to install, activate, and upgrade in place an activated copy. Last week I figured I would try using that same Win8 key to activate a "clean" install of Windows 10 for Boot Camp on my Mac Pro, and IT WORKED. I literally entered the Win8 key in the DVD box when it asked me for it during the Windows 10 install and as soon I logged in the first time I checked the computer information and it said I had an activated copy of Windows 10 Home(the Win8 was a Home version). I do not know if the original computer that I know of that had Win8 installed and activated using this key is still considered to be running an activated copy or not. My father does not use that laptop anymore, and I am not sure where it is. My point is, I do not know if doing this will make the Win8/Win7 installs on the original PC's will be deactived. Any more questions you have feel free to message me or if I was unclear about anything let me know and I will try to clarify.