When I did, I also bought it one by one.

It was mainly based on the requirements of the key, the original song that I wanted to play was based on and also the Octave in which I wanted to play.

The biggest flute I have currently is a C# and then in the order of decreasing size D, D#, E, F, F#, G, G#, A, A#, B, C, C#, D, D#, E, F, F# and G

This has proven to be enough till now for me.

I’ve seen flutes going upto A at both ends.

I think there’s no limit if the flute maker is creative and the player talented enough. I’ve seen Ashwin sir playing Ocarinas and Ney flutes with same proficiency.