I was looking at this drawing of a Roman soldier (copied below)
About the boots: Is this pair of boots plausible for a Roman soldier (in any era/province of the Roman Empire)? I would like to confirm the historical veracity of the picture.
These boots are in the calceus style. As such they are quite spot on and accurate for a Roman soldier in colder climates. But not unlike the caligae we stereotypically associate with a legionaire's outfit these type of footwear were also found across the entire empire.
via an ugly site
The actual styles came in quite a variety, though:
"Replikat römischer Schuhe aus Vindolanda - gefertigt von Meister Knieriem" by Hiltibold
So regarding the era and provinces: this type of dress is not that typical for a common soldier of the republic, but early empire, since the dress/armour would have changed as well in later times. But this type of footwear was well in fashion throughout the empire:
According to Simon James – who basically focuses on the Julius Terentius wall-painting from Dura-Europos – the following elements determine the Roman officer: the cloak, the tunic, undergarment, breeches, footwear (the calceus), the purse, but most of all, the sword on a baldric, the military belt, the golden finger-ring (the annulus aureus), and the military staff.
2nd and 3rd century AD depictions of soldiers. Attributes determining the Roman officer
Marie-Louise Nosch: "Wearing the Cloak. Dressing the Soldier in Roman Times", Ancient Textiles Vol. 10, Oxbow Books: Oxford, Oakville, p 93.
And in the age of Trajan, found on his column: