A big part of my take on the Xenorats is that they stay close to the character and form of their Skaven predecessors but incorporate the 40k themes of hopeless entropy and endless war.
To that extent, their ships are built by their combined mega industries of slavery and strip mining but they're technologically basic, frightening cans based off of bulk freighters and haulers that the vermin themselves have endlessly copied and remodified from ancient but robust STC design housed on their home planet.
Essentially they look like a cross between a D-day lander and an oil tanker.
In void combat they resort to brutal, large scale boarding actions, with Clan Admirals sacrificing dozens of ships so that dozens more can disgorge their living cargo on to an enemy vessel and claim it as a prize.
Their simplistic, Imperial pattern design often enables them to make planet fall by bluff and plant seeds of a new warren with maddening results.
On planet fall they disgorge hundreds of thousands if not millions of near starving vermin through their opened ramps, who quickly take to ground, vying to earn their lord's favor (or maybe even break away) by founding a glorious nest.
In the same way that their ships are a sickening mirror of the Empire, they're guided by Greylings, who act as their psykers, priests and astropaths. Since the rat men are born in such great number, they produce many psychically sensitive individuals, though routinely of a low power. Picked from their disgusting heaving welp piles, these Grey furred aberrations simply inveigh their God for protection and guidance through the warp for the entire journey. Prestigious ships often stock multiple Greylings for long distance travel, burning them out one by one in an maddeningly piteous and horrifying marathon of preaching and begging. Their success rates are near-chance, but there are always more, willing to find food and space for their endless young.