I love this suit and can tell I'll have it for a long time.
First, the fit: I'm 5'7", about 140 lbs, and have an athletic build. I got the medium jacket and size 4 pants. Overall, I had to make minimal alterations. The jacket fit great in the arms and shoulders, but there was a bit too much room around my body, so I had it taken in at the sides a little bit. The pants are a little snug on my butt and upper thighs, so I wouldn't want to have to carry a ton of stuff in my pockets, but they fit great around the waist. I had the length taken up about an inch or so. I considered going up a size in the pants, but I feared that if I did they'd be too big around the waist and butt and I'd have to have more alterations made, so I'm sticking with these and hoping the linen loosening over time will give me a little more room.
The material: Super high-quality. Love the lining. I did expect it to be a bit more breathable than it is? I wore it to a wedding in Portland, Oregon, in June. The weather was supposed to be 70s and ended up being like 90. I was sweating pretty heavily in this, but then again I think you'd be hot in anything at that temp.
The color: I love the tan linen because I think it's great for spring/summer. I wore it with a light blue linen shirt and brown shoes, and I think that combo made it a little too "retired dad" for me. I think a fun patterned shirt would help you avoid that.
Overall, I love the suit and definitely plan to invest in another from kirrin finch when I can afford it.