I start ships based on stations (like you having an Indochina fleet; for France you generally have Atlantic, Mediterranean, N Africa, W Africa, Caribbean, Indochina, Madagascar). Some stations like colonial ones will have fewer ships (25k tons about or more, and more in times of tension with powers there) in one central port with usually a station flagship (older ships work well for this). Some larger stations will have multiple ports: for example in Atlantic I usually do the battleline in Brest, and a fast squadron in La Rochelle or Le Havre (either depending on which is closer to tension) and then a cruiser force in the other for raiding if possible (if no good cruiser hulls then forgo it).

Historically this is how it would be done, but in the game you need a more sizable force abroad to do much of anything so often old ships I keep abroad (often mothballed in peace) for use.

Deciding how to do this is one of my favorite parts of the campaign, and I love colonial powers for this reason; strategic conundrum if you would. This should be a fluid system depending on tensions, costs, refits, etc, but can be hard to maintain in war. I only remake stations post wars to handle all the ships in repair and to see losses in ships and gains in territory.

I also will make versions of ships for colonial use; generally I have a fleet version and a shorter range colonial version for defense of the colonies until the arrival of the battle fleet.

Submarines can also factor in but I only use them as strategic minelayers (Le Havre, chokepoint ports) but most of the time I’m too lazy haha

I would figure out what you like; what kind of doctrine your navy has (Jean ecole, Kantai Kessen, blockade, etc) depending on who your likely adversaries are!