There seems to be a lot of confusion about season and D4. So let me explain.
D4 seasons is quite similar to D3 seasons, they are separate from your regular characters. Yes, they start off level 1, and you progress through the battle pass, or whatever new gimmick they hatch for the season.
When that season is complete, your seasonal character is transferred to your regular characters, and everything you have obtained goes with it, all gear, gold, etc.
YOUR REGULAR CHARACTERS ARE NOT DELETED. They will still be there.
I repeat, SEASONAL CHARACTERS ARE SEPARATE FROM YOUR REGULAR CHARACTERS!
The character you create on launch will not be deleted, or set back to zero.
At character creation, you will be able to chose between a regular character, a seasonal character, a hardcore character or a seasonal hardcore character. If you chose a seasonal hardcore character, at the completion of that season, that character will join the other hardcore characters you have created.
Seasons are OPTIONAL. You do not have to do them, you just wont be able to get the perks from doing the seasonal content.
Personally, I think July is a little early to start seasons, but whatever.