Feel free, but out of personal observation, Plethora would take the chance to wipe the floor with you fairly quickly.
Not so long as his nation didn't overlap with
Avalonia's planned conquests (plus a couple islands between Hokkaido and Kamchatka that I missed) over the next several decades. If he were to start West of Lake Baikal Avalonia would have little reason to attack unless provoked.
Avalonia will allow amphibious landing testing on its shores once there are existing landing boats that work. The Khan sees no reason to waste the time and lives of Avalonian or Erinamese sailors and engineers on landing tests until the boats to be used can at least stay afloat in the ocean. In the meantime, however, Avalonia will attempt to assist Erinaum in its venture provided that Avalonia be able to benefit from this as well.
Meanwhile, Avalonia continues construction of a more conventional fleet of troop transports, warships, and military supply ships.
Avalonian forces push across the Strait of Nevelosky by boat (where Asia and Sakhalin almost touch) and encounter little or no resistance as the entire island seems to be fairly barren, sparsely populated, and poorly armed. Avalonian forces pushing south into Hokkaido encounter greater resistance as the population is more heavily armed than their northern neighbors and also more isolated from Avalonia in past leading to Avalonia's lessened ability to count on surrenders caused by Avalonia's reputation. Avalonian troops use tactics to exaggerate Avalonian strength such as lighting extra fires at night, having captives ride spare horses, and dragging smaller tree limbs behind to raise dust to make the increasing Avalonian forces seem extra formidable. As the Avalonian reputation spreads, more local fiefdoms choose surrender rather than death.