I was wondering if someone could educate me on how to get into the Mac pro scene. I have a 27in Thunderbolt Display hooked up to a MacBook Pro right now. Only video editing I do is on Imovie for family stuff. Won't and can't spend 3,000 on something I just want to dip my toes into. So I want something used that is expandable and can tolerate 16gb of ram. Also I am not a heavy gamer. Any help to this rookie would be appreciated.
"I was wondering if someone could educate me on how to get into the Mac pro scene."
This sounds like you really do want to go the MacPro route.
Let me say up front... I'm thrilled with the new MacPro6,1 model and have two of them. I've owned every MacPro model since the G3 PPC model.... G3, G4 and G5.
OK then, treat yourself and scan Apple's MP6,1 4-core refurbed models. At this time the least expensive MP6,1 4-core on Apple's refurbished site is $2549. Or you could try Adorama who has these models for around $3000 with free AppleCare and zero tax if you're not a NY resident. This 4-core can be upgraded to 16GB RAM by adding a 4GB module.
You already have a 27" TB display so you're set.
The footprint of the MP6,1 is very small and will not clutter your desktop and for the most part is inconspicuous in its black look vs. white such as the Mac mini.
Don't even look at the MacPro4,1 or 5,1 models. They are monsters (size and weight wise) and yesterday's technology, eat too much electrical power, lack Thunderbolt and USB3 and use lessor performing Wi-Fi. Moving one of these monsters will likely break your back and hog dust like crazy. They lack AppleCare for the most part as well. Don't get sucked in with people saying the MP6,1 cannot be expanded. The older MP4,1/5,1 models can also get noisy with all 5 fans spinning at times. The D300 in the 4-core will be just fine for your iMovie. SSD and RAM can both be expanded, and even the CPU can also be upgraded to have more cores if you want. You can hang 36 Thunderbolt drives off the MP6,1's 6x Thunderbolt-2 ports if you want. Enough to last you a life-time. HDMI port for your big screen TV if you want also. Buy used LaCie Thunderbolt-1 drives (gives you at least 350 MBytes/sec) to keep cost down.
The MP6,1 will give you years of use.
OWC provides upgrades for the MP6,1 so if you want to expand it that's not a problem.
Enjoy life and get yourself a MP6,1 4-core. You will not be disappointed IMO.
I have MP6,1 12-core and a MP6,1 6-core. The 12-core has been operating for a year now without a single hiccup using Adobe CC primarily. The 6-core is a recent purchase made late last Dec. These are used for business and they are the best MacPros we've owned since the early G3 models. Mind you, the previous MP5,1 were also awesome to use, but now are really dated and will lack making use of the future technologies.
As far as I'm concerned, the MP6,1 will take on just about anything you want to throw at it. It will not 'bat an eyelid' and will run all day long at full load.
You might find your current iMovie use will move up to the more professional FCPX which excels on the MP6,1.
I say again, treat yourself and enjoy life with the MP6,1.