The fit part is accurate. Color advice depends on more than just hair color. For example, pale skin and solid white tends not to look good, though there white needs to be worn occasionally. For "business casual," checks should be fine. Maybe even better than stripes, for stripes on a thin man who isn't wearing a jacket can make him look thinner. Most patterns should be a mix of blue and white. Maybe also purple or pink on white.
A cotton blazer (technically, a sport coat, not a blazer) might be comfortable, but it very likely is too casual for the office. Tropical weight wool or perhaps with wool with a little linen would be better. Half-lined could provide extra comfort, too, but virtually unlined probably would look too casual.
Agreed on not buying a fedora. On a young man, that usually looks like costume.
The jacket should be an overcoat or topcoat, to go with a suit or sport coat.
I agree - my advice was intentionally a bit more quick and dirty. Pay a great deal of attention to what colors look good on your complexion. One thing you discover there (especially if you're a "midwestern" complexion like me) is that white and black tend to be very overused as shirt colors. If anything, think more in terms of off-white, and by this I especially mean DON'T DISCOUNT PINK. A very light pink looks so flattering on so many people. Don't be afraid to try it. An ideal discussion as to the "why" behind all the coloration is in the opening section of "Dressing the Man." That section on framing the face through colors is worth the book by itself. Bottom line, there will be good colors and bad colors for you and you have to (but can) figure out which is which - no cookie cutter works for everyone.
I'd second getting your first jackets out of wool, not cotton or linen. You want something that you can wear as year-round as possible, and cotton or linen does look and feel a bit weird during a snowy winter. And I agree that the topcoat is the priority among jackets, though you'll require at least 2-4 scarves to wear with it and you'll want something else that you can rotate with it on non-suit days. The coat section might be more expensive than you think.