There won't be a character wipe.

I don't know how much experience you have with Diablo games, but don't worry.

When a season kicks in, you will have to create a new character, your old chars won't be affected, they just won't be seasonal characters.

The game will have a another "realm/world" that will be for seasons, and the "Eternal" realm/world, this is the one where your current characters will remain.

Check when you log in the game. That this is the name of the current world you are playing.

Even when playing a seasonal character you will be able to get to your old one and finish things up with him. This will not affect and/or progress anything on the season achelievments/mission thought.

On D3 we have something called rebirth where you just reset a normal char into a seasonal one, this was nice mainly because some players like to keep track of the amount played with the character. And to save a character slot.

Nothing to worry, keep playing and unlocking everything you can.

My tips is to finish the campaign, so you will be able to junp directly into the seasonal content and open up the map, map, renown and Lilith statues progressions will be shared with the seasonal character.

Hope this helps.

Ask away if you have any questions. Now...

Go slay some demons! =O)