Now I have some time to look closer at it - all I have done before was (ab)using some time between meetings and stints in a clean room. Hey, at least that way I got payed for it
Looking at the data sheet of the transformer, I see it's a tiny 30VA one. Looking at the fuse ratings on the primary side I expected quite a bit more power. The data sheet states those "recommended fuses" belong to the secondary side, see the fine print, footnote number 3. And it even states the reason, UL class 2/3 operation, and places me deep in CE-territory where UL is not of much concern. A fine point learned for me
So, you should recalculate the fuse on the primary side (and add one on the secondary if UL-territory is an issue).
As a transformer is a hefty chunk of metal, are you OK with the bending and shear forces on the PCB and the M3-screws if the case containing the PCB gets dropped or just handled roughly? I would think about two more screws at the middle of the PCB to reduce the bending forces. The four holes through the transformer core are there for a reason, but it would be a bit much using those additionally to fix the transformer. Another option would be using those holes in the transformer core, with distance pieces to the case, to mount the whole assembly, not using the four screws now present. The mass of the PCB and the terminal blocks is negligible compared to the transformer.
BTW, the Board v.0.2 is a bit hard to load, the "drtebi.com"-part of the link is missing. (I got it anyway.)
It looks a lot better (or, at least, more to my liking..), the etch-traps on the secondary side are still present. Join those tracks at right angles, not 45° (or, in this case, use copper fills).
The voltage regulator should do it's job, but the person drawing the schema on the website should learn how to do it, and the text contains a bit of audiophile-crap like "The RC filter before the voltage regulator unburdens the regulator from having to deal with sharp transients." Hell, exactly that is the job of the regulator: Keeping the output voltage as constant as possible, and that as fast as possible - that's how to deal with "sharp transients".
(Audio and "sharp transients", that needs much imagination in itself. A constant current power supply (0..10V in, 0..100A out, 2kW sustainable) able to hit a load with 3000A/ms, that's a "sharp transient" in my book. )
Now, 10 seconds meditation to let the blood pressure drop again. Done:
That's perfectly OK. You have 1.6mm Glass and Expoy in between.
Not "as much as possible", dchisholms solution is about what I would do.
I would change the layer of Net-(S1-Pad2), connecting pin2 of the switch with pin 2 of the transformer. You have "L" connected to the lower row of the switch, and would never have leakage current issues from that trace to Net-(J1-Pad2).