30.
I dont know how reliable my assessment is to be honest. At first it's hard cos there are some rules that are to be followed, but after a while it became like a sudoku to me. If you follow the rules correctly and are patient enough, there is always at least 80% chance the chain will continue. Its really fun for me too, you get to know some parts and routes of the game a lot more, and idk, it beomces a lot more personal. its not just "that route". Its the freakin' route where you caught something really cool.
Ooooh I also forgot my Shiny Eevee (18th chain ^^ ), now Shiny Umbreon :D
Anyway, I suggest going through some youtube and written tutorials. its not too hard, but not entirely too easy either. :D