Complete set for deep sky astrophotography

What are your goals for this "deep sky" system?  What size focal length are you desiring to use?  The longer the focal length the more stable/robust your mount system needs to be in order to obtain long duration exposures..  It eventually becomes not very portable…

I'm assuming you are referring to a Canon 5D mk IV camera. One thing you must be careful about with a full frame camera is that it has a ~43mm diagonal sensor which is larger than most telescopes are designed for. Most people use either APS-C (~27mm) or Micro 4/3 (~22mm) sensors, and that is the image circle that most telescopes cover. Unless the telescope you are looking at specifically says that is flat field for full frame, you must research the size and flatness of the image circle. Most telescope designs will require you to purchase a optional field flattener or reducer/corrector (corrector is just another name for flattener ) to make the field flat. These devices usually reduce the image circle, so you should be checking on the image circle of the specific combination of telescope and flattener your are interested in.

Three small scopes to consider that people have had good results using with a full frame camera and also travel well are:
Samyang 135mm f/2 ED UMC (also sold under Rokinon brand name)
Canon EF 400mm f/5.6L USM
AstroTech AT65EDQ  (420mm f/6.5)

For beginners shorter is better because it is not that easy to find things in the sky.

OK - just to clarify though I think you might be confusing focal length with objective lens size.  A 100-120mm focal length is not really long enough to capture much detail in those Messier objects you mentioned.  In fact, that length is really nothing more than a camera lens.   I think you meant you are looking for a telescope with a 100-120mm objective lens size which would equate to roughly 600-900mm focal length….depending on the F-ratio/scope brand etc.
So if I am correct in my assumption then I think eventually you will find after researching that a scope of that size won't be terribly portable, once you consider the mount that will be necessary to support it along with a camera (full frame Canons are kind of heavy) along with a quide-scope which you definitely will need at that focal length, etc.  You'd need a hefty power supply and laptop to run all the software, with associated wires, etc.  it's gets rather unwieldy quite quickly.  You can save some weight with a carbon fiber scope, but I don't think William Optics carries those (Explore Scientific does though, and their scopes are pretty good and reasonably priced).  I have the Explore Scientific 127mm carbon fiber scope and really like it.  I have it on an Orion Atlas mount and just moving it from my office to the front yard is a chore.  I don't think I would enjoy packing it up in a car and taking it somewhere….
If you are just starting out - I'd recommend learning just using your DSLR and a quality lens - 50-200mm.  Get a solid tripod and something like an iOptron Sky Guider Pro for tracking.  Or even an Astro-Trac.  You can get some very nice wide field images with that setup.  If you really get hooked, then look into an EQ mount and telescope package - but I'd stay at an 80mm Obj lens type of scope at first - this will equate to roughly a 400-500mm focal length.  You'll need a guide scope as well at this point.  If you still have the bug, then move on to a larger scope….sell your previous gear to help pay for the larger scope.  But i think you'll find a 500mm focal length will keep you busy for years….best of luck. Go slow and learn as much as you can.  The capturing and processing are a large learning curve.

I would recommend to start from the basic Newtonian scope (yes, I like Newtonians despite constant re-collimation and coma), for example 130/650 or 150/750 and decent equatorial mount (Skywatcher HEQ-5 or 6), short-tube Orion guiderscope and guiding camera, Barlow2.5-5 and you are ready to go! Yes, your camera will have a significant vignetting due to the size of the matrix but you can crop the final image. This setup will be about $2000. You can observe, do planetary video-imaging and shoot DSO. You can choose small APO as a main scope, better to start with 80mm-420/480 mm f5-f6, but with flattener the scope only will be over 1200-1500 (again there are a lot of cheaper Chinese clones available). But more important: stop reading and start acting, clear skies!

THANK YOU ALL for helping me with this. I've been looking and reading about all your recommendations. Very Helpful! If any of you know of any video link that could be informative for my situation, please let me know. I rather watch something recommended by an expert than just watch anything that comes across. Thanks again! - R

An important specification that you did not quantify, is what do you mean by "portable"? Reading the various recommendations above, I realized that different people have made a good recommendation for different assumptions of what is portable. A good guideline for categorizing basic operational weight including scope, mount, guiding accessories, finding and calibration accessories (e.i. GoTo, polar scope, etc.), mount hardware (i.e. tripod, pier, etc.), cameras (i.e. imaging, guiding, etc.), and control hardware (e.i. personal computer, controllers, communications, etc.); but excluding cases, furniture (i.e. tables, chairs, stands, etc.), and vehicles (i.e. trailers, vans, RVs, etc.). Is under 50 lbs. (which is considered air portable by many people only because you can't do this with much under 50#), under 100 lbs. (which is an entry level weight class), and under 200 lbs. (the beginning of high quality equipment). At star parties I meet lots of people that haul around imaging systems way over 200#, and they think that is portable.

I assumed under 50# and "100mm" meant focal length, so I recommended camera lenses, which would work with other people's recommendations of trackers  such as the iOptron Sky Guider Pro, Sky-Watcher Star Adventurer, or Astro-Trac.

Other people assumed under 100# and "100mm" meant objective diameter, and made recommendations  such as the  iOptron iEQ30Pro, Sky-Watcher HEQ-5 and AZ-EQ5.

Finally, there are a few under 200# recommendations such as the Sky-Watcher EQ-6.

While most mounts are rated by payload, the real issue is moment of inertia. An 8" SCT can have a smaller moment than a 6" Newtonian or a 5" APO refractor. A short, fat SCT has most of the weight concentrated around the primary mirror; while a long, thin Newtonian or refractor has the weight concentrated on the two ends, glass on one end, camera on the other end, and air in the middle.

Well suggest Newton 150 or 200 with F5 they cost nothing, 150 is much more portable, mount - HEQ5, thats about 1800 $ then you will need power tank thats another 149$ + you need camera adapter thats another 30$ + youll need guide scope or offaxis, suggest offaxis - less weight,  much cheaper than guide scope = starting from 90$ + youll need guide camera  i use cheapest - zwo asic 120m nice camera for a price of 200$ in total thats about Your price
p.s. sugest a 1 cm ring for guidecamera, because it need longer focus than provided with offaxis dye to difference in sensor sizes, thats another 30$ still close.
p.s.p.s. in my opinion best choice, newton need collimation if transported brutally, but once u know how to do it, its easy with collimation cap (can make yourself) or by later collimation laser.
p.s.p.s. need a remote for camera to work in bulb mode (on Ebay costs 9$) + suggest to buy another battery for camera, because best time is in winter when it is cold, and in cold those damn cameras lasts only for 40 - 50 minutes (-15 C)
So i think thats all you need + about 20 nights to learn how to use all that  Good luck, will follow Your progress!!