The Garrett Files are great for the first few books, like really fun to read and fairly original, then they get pretty repetitive, but they are still worth a read here and there. I can't say how they would be all in a row, more stuff would make sense probably, but more stuff would get old really fast too.
Some of his other books like Starfishers and such didn't really catch my attention and I've only read a couple. The Dread Empire stuff is ok, but clearly inferior to The Black Company (my favorite books of all time btw), so you might want to hold off/skip those for awhile unless you're dying for something to read. There are a lot better books than those that do much the same thing.
Instrumentalities of the Night I could only read the first book, and it was absolutely horrible. Imagine a history book telling you the geographical, religious, and political histories of a country for the last hundreds (maybe thousands) of years. If it were one you were familiar with, like say something in the Middle East just as an example, it would be hard enough for you to follow even if you've picked up some of it over the years. Now replace that with an entirely fictional world and fictional people. Imagine that goes on for hundreds of pages. That is the first half of the first book. It sort of picked up a little from there because it actually started to focus on (still too many) characters, but it was still atrocious. Maybe the next books did away with the "world building" and got better, and I'm sure some people love that level of detail for some reason, but fuck if I'm going to ever try. And this is coming from someone that just said some of his other books are my absolute favorite. I was so disappointed by that book. The Black Company is my favorite because it is so sparse on detail that you have to fill almost everything in with your own imagination, and it works perfectly. Instrumentalities is the exact opposite, where not a single thing is left to your imagination, and it is practically like taking a college history course on a fictional world. Fuck that book right in the ass.