Tuner then synth then dirt.
Wheb they say that the synth needs to go first, they’re more likely talking about engaged (as opposed to bypassed) pedals as having another active effect before it in the chain (eg distortion) would mess up the tracking. Probably doesn’t matter what order if you were only using one at a time.
As I said before, you might wish to have the synth running into the distortion as post-filter distortion can sound amazing.