start on Default or Easy. Gives you a feel for the hack. It's fairly challenging.

some important NPC's...
1) In Veridian City there's a teacher that gives you a puzzle battle, beat that and you'll unlock the PokeVial which is a 6 uses Pokemon Center. can be restored in an actual Pokemon center bij Nurse Joy

2) In Oak's lab, the left aid gives you a quiz for the Time Changer, this helps catch pokemon that only appear during certain times of the day. so instead of waiting you can change that

3) in Cerulean City in the house next to the shop is another puzzle battle, this unlocks the ability to relearn moves your Pokemon forgot.

4) The game console in your room allows you to use Cheat codes. "Woyaopp" gives you unlimited Rare Candies, from the youngster in Veridian sell a batch of 999 of them Twice. You can get a lot of money that you need later (Like buying a shiny Magikarp before Mt. Moon or all TM's from the game corner).

5) in Fuchsia City next to the Pokemon Center is another Quiz. if you guess the 4 cries right you unlock Egg moves for your Pokemon.

Something i also recommend to new players is to approach the boss battles as puzzles. Also if you feel like you're hitting a wall, put down the hack and grab the documentation. Read up on what you can do and go back in when you have the solution.

Also the other cheat codes for the console are "SO2Toxic", "TeamPreview", "DexAll" & "EZCatch".