Hello, I have been researching this all summer, just received those same coils and mattress cover, and have some insight.
First of all, you may or may not like latex. For sidesleeping, I found the pushback of 24ild talalay pushback on those exact coils and mattress cover to be a bit too much in terms of pressure points on my hips / sciatica (though maybe 19ILD would have been better). My partner also agreed. However, that in no way means that you cannot use the latex 
According to the successful builds megathread at Reddit r/mattressmod several people are combining latex with foam (i.e., polyfoam, memoryfoam, enregex, viscofoam, serene foam) either above or below latex layers to get the support of latex but negate some of the pushback. This is what I plan to do next. I am not sure if you are familiar with this counterpoint about latex, but it is worth thinking about to inform where your build might if your body responds the same way.
With that out of the way, here is my feedback about the coils and mattress cover that MFC sells that I ended up purchasing from their neighbour Nature’s Embrace (purchased together as their Essence model .. more on that later):
7" Caliber Edge Coils
The coils feel great. I spent a lot of time trying to figure out how they would feel in comparison to my old Springwall pocket coil that honestly feels great (though starting to become plushy after 8 years – which could also be the comfort layers). They feel medium firmness to me which is what I was after. Actually, they feel like how my Springwall coils used to feel, and I wouldn’t be surprised if they are actually the same L&P coils (I believe L&P manufactures coils in Ontario?). They are in fact 7" which differs from the common L&P 6" coils that dominate forum discussions. In trying to research the coils, many people seemed to prefer the slightly firmer feel of the 6" coils over the 8" L&P coils. In theory, these 7" coils would sit in between that firmness range? The edge feels supportive but not noticeably different i.e., can sleep on edge comfortably.
Versus TPS coils
I don’t have direct experience with TPS coils. In the DIY community on reddit, the 15.5 texas pocketspring coils are the most popular, but they are incredibly hard to get in Canada – and with the new tariffs on steel, expect to pay more than they are worth when coupled with very high shipping and broker fees. And they don’t ship to Canada, so you would have to figure that out. Also, a very common complaint about them is that they can splay out without the right mattress cover. However, one Canadian user successfully used them using just the TPS coils and their microcoils contained in that very MFC/Nature’s Embrace cover, and then used latex layers above that. I bring this up because, even if you decided that the coils weren’t for you, you can still use the MFC/Nature’s Embrace cover for the TPS coils. So far, I am very happy with the coils and see no reason to switch to TPS. The fabric on top of them is pretty flimsy, but in the mattress I bought, the coils came in their own jersey cotton cover which should help protect the latex.
Mattress Cover (MFC / Nature’s Embrace)
The mattress cover is nice and stretchy which is what you want in DIY cover. The tencil top feels and looks great. I can’t speak to longevity yet as I’ve literally had it for 24 hours lol. There are no handles and moving the mattress once built is kind of a pain as I discovered last night. The main downside I see to your build idea is that if you need more than 10" of height (i.e., 7" coils, 2" transition, 2" comfort) it probably isn’t going to all fit in that mattress cover. I am guessing there is still enough room for a 1" foam layer which is what I am trying to figure out right now. Honestly, I can’t seem to find Canadian source for the 1" serene foam I am after. If you need more than 1" it would have to sit on top as a topper unless you sourced an additional mattress cover. It is worth mentioning that several users at reddit compartmentalize layers; so despite the higher cost, the strategy of using more than one cover could actually be a good thing (i.e., layer protection, structural integrity).
The Presto mattress MFC mentioned is built for a taller build (i.e., both the comfort and transition layers over the support layer) and has features you would be used to, like handles and a more substantial top (lacking in the DIY mattress cover). For $1600 it seems reasonable and you could presumably swap or add a foam layer to combat pushback if that becomes an issue. However, I do not have direct experience with that exact mattress.. just comparing the pros and cons as I considered it too.
Canadian suppliers:
What might work for you is to purchase the Essence Mattress from Nature’s Embrace. It includes those same 7" caliber edge coils, a layer of dunlop latex in your choice of firmness that qualifies for their layer exchange program, and that same mattress cover you mentioned. In doing the math, it seemed like I was getting the dunlop layer for free versus buying these components individually. However, MFC seems to have better expertise / customer service. I was also looking at Dormir for dunlop latex. One user I was chatting with on Reddit had success with their medium dunlop latex layers over existing coils from an old mattress. However, there is a cost saving when going with either that MFC Presto or Nature’s Embrace Essence mattress versus going complete DIY by purchasing every component individually.. not to mention the peace of mind that these layers are sold together all the time for this very purpose.
Looking forward to hearing what you chose to do and how it works out for you.