I have two CX. One is single speed (not fixed) and one multi.
As for fixie? That is a no on the trail as you lose ground cleareance. With roots, rocks, and drop offs you need to stay on top of the bike. I have single speed mountain bike that I would hate as as fixie.
That is a light racing style frame with carbon fork. Decide if you want to go for weight all the way. You could run an aluminum drive train and race tires like a Cyclocross Speed and have a solid cyclocross bike that does road. Or go with more durability and steel drive train and heavier non-racing tires.
A single speed CX works but the hard part there is gearing it. If you gear it for the top end you don't have enough low end for a steep accent. It is easier gearing a single speed mountain as it does not have the top end. Top end from street is taller than top end trail. Up front use like 36 - 42 chainring. Fairly easy to swap out the rear and the common sizes there are 16, 18, 20. Pick a chainring size that lets you best go from road to trail on the freewheel.
Get CX not road wheelset. Don't cheap the wheelset.
On tires you can find some that go both ways nicely like a Continental Travel Contact.
Change the pressure from road to trail.
They make racers ride in the mud but if this is your city/trail bike then just don't ride it in the mud.
Two wheelsets would be convenient not just for tires but to gear them them differently.
But I would put my money in a one nicer wheelset and a White DOS freewheel.
That frame is set up for cantilever so that decides the brakes. I like disc but you don't find many CX set up for disc.
Clipless (as in actually clip like SPD) over a downhill or flat pedal.
The reason there is little more torque with the push and pull.
It can save you from stalling out on an accent.
I run the bike in the picture below on road and trail. It has 35mm pilot city tires but I ran it on cyclocoss tires for a few years until I got tired of replacing them. I change the pressure by 20 psi as I move from street to trail.