I have that pattern, was it difficult?
It wasn't "difficult," but it was time-consuming -- there are 71 steps, if that tells you anything. Also, I'm useless at cutting around pattern pieces, so this is what I did to make it easier for
me: since most of the pieces are rectangles (except for the front flap and the pocket flap), I measured each of the pieces and wrote down the measurements. Then, I used my
omnigrid ruler and
rotary cutter to cut perfect rectangles. I understand these are tools that not everyone has (I'm a quilter) but they really do rock for cutting perfect squares and rectangles, especially if you're like me and have a hard time cutting a straight line.
However, my difficult in cutting straight lines is not shared by everyone, so this might be easy for you.
Okay... after I got the pieces cut, then I just went through the steps, very carefully. I would recommend reading the pattern ahead of time, slowly. I got overwhelmed several times when I first got it, but by taking deep breaths and reading it carefully, I figured it out.
However, I just remembered one other change I made to the pattern. They didn't have me adding the velcro inside of the flap until the last step. This would have made the velcro sew lines visible on the exterior of the flap, which I didn't want (and is not how it looks in the picture on the pattern). So I sewed the velcro to the flap lining before sewing the flap together. That way, the velcro sewing lines are hidden between the flap lining and the exterior of the flap -- does that make sense at all?
The one tricky part for me was the hand-sewn slipstitch on the flap of the side pocket, but that's only for a couple of inches and ends up being nearly invisible. Plus, I understand that not everyone hates hand sewing as much as I do.

Also, it's kind of tricky using that thick, thick fabric (the fabric I used was a sailcloth, which is thick on its own, but with the fusible fleece on it, it's very thick). In fact... I used a
walking foot, which is a foot used for quilting because it feeds the fabric evenly on the top and bottom. I don't know if it was necessary, but I think it helped a lot, especially on the parts that were quite thick.
I hope my verbosity has not scared you away. Even without the fancy tools, I think that a beginner could get through this pattern by being careful and taking it slow. As my friend pointed out, "It's basically a messenger bag with a lot of pockets." There are some great tutorials on craftster for making basic messenger bags, so you might want to look at those, as well.
Where did you find the fleece stuff?
Joann fabrics. It comes in a package and it was with... notions, I guess. Near the velcro and whatnot. It's made by Pellon. I think you can also buy it by the yard, but the package was the size called for in the pattern, so that's what I got. If you can't find it at your local fabric store, just ask -- they'll probably have it.
Edited to add: Oh, YAY! While I was typing this (rather long -- sorry!) response,
TheBon posted her response. I am SO glad it came today! And I'm glad you like it!!