Not sure what you mean by thinsulate with nylon shell, or what is a "fleece pattern".

You need an outer layer, insulation, and inner layer. The outer layer has to just a bit bigger so that the insulation is not squished. If the insulation has an already attached nylon side, that becomes one of the layers. The outer and inner layer material used can make a big difference in the total weight of the jacket. If the "jacket" is to be your outer layer, then you need material on the outside that is tough enough to withstand a bit of bashing, such as rip-stop. The inner can be UL and a bit more fragile (taffeta is often used). If the "jacket" is going to be used like a sweater under another layer of clothing, then both inner and outer jacket linings can be very light.

Patch pockets are a lot easier to sew than pockets that insert (cannot remember the term used for these). A patch pocket is just a square sewn on top of the layer. Think about where you want the pocket. I find that patch pockets attached to the inside of a jacket will securely hold stuff without adding a zipper, whereas on the outside I would put a zipper.

You might just go look at a commercial thinsulate jacket and examine the sewing on it to see how it is put together. A lot use large quilting triangles to keep the insulation in place. I am not sure what expanse of thinsulate you can have before it tends to shift on you, especially when washed.

Every stitched thinsulate to layer makes a cold spot so you do not want to use these in excess.

I do not know how much sewing you have done, but getting the sleeves attached properly can be difficult. I think if you just put all layers flat together, you are going to get lumpy sleeve seams.

But if you already have the material, at a minimum it will be a good learning experience.