So.
I'm going to be running a steampunk/Dying (not)Earth campaign. How soon is not too soon to give the PCs their own airship?
It will be lighter-than-air a phlogiston-lifted dirigible with spring-powered propellers.
Also, what is the best way to reduce the number of crew needed? DM fiat? They usually need a crew 10, but I'll only have 4 or 5 PCs.
Not sure if it would work in your worlds, but... permanent Unseen Servants dedicated to the more mundane tasks?
Or you could have some steampunk-esque Rube-Goldberg device to perform tasks from one or more control panels.
I'd give them flying vehicles around the level when PC classes unlock flying abilities (like spells and wild shapes that allow flight) and at that point they should be able to pay few hands to fill out the crew quota.
So, around 5th level?
That makes sense. Especially in 5th Edition, where 5th level is a major power boost.
Would a living airship be cool? Either an airwhale or skykraken?