Excellent! Well done! If you have 180V, then that is the hard part already done!
You can go on and mount the rest of the components on the main board, apart from the WiFi parts and the tubes. These are easy and should mount with no problems.
If you are as impatient as I am, you can also have a go at mounting the "seconds" tube holder. The heat of the tip is more important than the size of it, but do what makes you feel most comfortable. 3mm is pretty large.
Another option for soldering the LEDs to the tube boards is to use solder paste. I did this the last time I put together a modular and it worked well. I used "Kester 356 Sn63Pb37" paste which flows at a cool temperature of 450F / 240C.
Press the LED into position. Apply a small amount of flux to the LED pins. Squirt a tiny bit of paste (from a syringe) to form a bridge from pin to PCB pad. Touch the paste with the iron tip just long enough for it to turn silver and flow. Inspect to make sure it formed a bridge and not just 2 dots.
Look into it later when the dust is clearing off the crater.