I actually made the interlining removable, having made the coat first and thinking it may not be warm enough. After I removed it I wondered why someone would want a removable interlining as they are a pain in the neck to remove and reinstall. I can recall my grandmother interlining coats she made for me with a chamois and then moved them coat to coat as I grew.
The thinsulate may work with the coat you have in mind but I think you may find that may be 'poky' above and below the belt. Most thinsulate I have seen used effectively have been in mittens and boot liners.
Myself, living here in North Central BC, where we get some VERY cold weather I have been making my coats out of polar fleece and lining them with a windproof nylon lining. I have been warm at - 35 C, providing I keep my hands, feet and head warm. Once I get out of my foot boot d/t surg I have a lovely grey blue fleece to make a coat. As I can't quite decide what style I have purchased 4 different patterns - they may end up costing more than the fabric!
I think that in terms of warm coats it helps to think about what is it that makes you cold - still temperature, wind, humidity? May give some ideas as to what to make coat out of and what to line with. As will what you will be doing when wearing the coat. The suede material will hold heat in, if you are warm when you put it on and will probably hold the wind and moisture out. You may think about lining it with a light weight polar fleece (an exotic pattern would be interesting). Remember the concept of what makes something warm is the air pockets which hold the warmth. A belted coat is also going to be warmer than a looser coat and the length will affect how warm you lower parts will be.
God put me on this earth to sew and finish a certain number of things. I am so far behind now.....I will never die!.......If I stitch fast enough does it count as an aerobic exercise?