Haven't found an answer to this question yet: how much Encumbrance would a vehicle take up inside a starship?

Just for example, I'd like to bring an airspeeder (probably skyhopper, Silhouette 2) or speeder truck (Silhouette 3) along from planet to planet inside my Citadel-class freighter (Silhouette 4). How much Encumbrance should I have left over out of the cargo hold? What if I want to bring 4 speeder bikes instead of one truck?

For that matter, how much Encumbrance does a single person take up? Just going on the Speeder Truck it can carry 225 Encumbrance or 20 passengers, leading me to believe 1 person = ~10 Encumbrance. But the Hidden Storage Talent is described as being able to hide 1 Encumbrance and also being enough space to hide humanoids on a Silhouette 4 ship.

People take roughly 5 + BRAWN in Encumbrance.

So I guess Hidden Storage is just a specialty rule in that case, since you can hide an unspecified number of humanoids (plural) in 1 Encumbrance using that Talent?

Yes, the Hidden Storage talent is a special case.

As for your initial question, I'd go with 20 times the Silhouette as a rule of thumb. The airspeeder may not be all that heavy in and of itself, but it takes up some space in the cargo hold. If you're dealing with smaller vehicles, like swoops or speeder bikes, I'd rule it as 10 times Silhouette. But that's just my opinion.