re: Please help me with proper leader selection
Not the same diameter necessarily but have the same amount of flex.
They should bend the same to eliminate any hinging
You really don't have to worry about it though. Store bought extruded leaders that match the kind of fishing you intend on doing will all be close enough.
The simpler the outfit, the more skill it takes to manage it, and the more pleasure one gets in his achievements.” --- Horace Kephart