If the stove is new, you can always return it. Just tell the retailer that your chimney and ductwork won't allow the use of this furnace.
As for a do it yourself install. If you are going to hook it into the ductwork, and have never done ductwork fabrication before, then I'd say hire the job out. When I helped a friend who needed an extra hand on a ductwork install, I was amazed at the different metal shears [left, right and straight] bending brakes, shrinkers, etc that he had and used.
If you have never installed a stove, wood burner, or other solid fuel burning device I'd get help. It is too easy to cost yourself more than the help would cost.
Are you planning on burning just coal in the furnace??? are you home to tend to the fire often? Any chance you have access to wood instead of coal?? Like I said earlier, the Hotblast furnaces are a compromise design. You will have to tinker with it, and learn it's characteristics when trying to get it to burn coal. I't will probably burn wood fairly well with feedings every 3-4 hours.
I copied many of the design features of the Hotblast, and other US stove boilers/furnaces when I made my VERY EXPENSIVE all stainless steel 'Big Bertha' boiler. Knowing what I know now I made a great wood boiler, and a fairly poor coal boiler.
What Dirvine96 said was good info.
I still think you would be much better off getting your money back, and getting a designed for coal appliance. In fact I HIGHLY recommend it.
Do a search on user name tigermanrich he has a similar furnace and has his own long tale of problems I would hope that you can avoid these problems
Give us some photos, details on your house, size, location, insulation etc,