Personally I don't think you should but it is up to you.
If you have chosen Bulbasaur as your starter then Gary chose charmander. Catch a water Pokemon to beat it.
Use Charizard And Legendary Pokemon. Train to Level 80. Beat Garyy Is Easy
on the top of mt.silver when you have beat Gary and his first Pokemon is a level 88
You don't need to start all over again, after beating him one (and getting 100 Pokemon for the National Dex) you will then be able to get to 4-7 in the Sevii Islands.
Gary until you beat him and then you get put into the hall of fame and you become champion
Gary (Or blue) is hanging out on Cinnebar Island, but you have to beat all the other Kanto leaders before you can challnge him.
on the s.s anne after you beat Gary go see the captian and he will give it to you
nothing you start again
when you beat the elite four and have 100 Pokemon go to professor oak and he will give you and Gary the national dex
You have to beat Gary and evolve kadabra with twisted spoon
It all depeds on the Pokemon. If you has a Water Type and he has a Fire Type, you can beat him. If you have Pikachu and he has a Rock Type, then switch it because Rock Type can resist Lighting Type moves. (I have this and I can't beat Brock!)
the Pokemon have levels not you