You get to keep your map level but when you turn to level one after choosing a perk, your current gear will be placed into the inventory (you need 8+ free inventory slots to ascend anyway) and you will be level one with level one gear.
Then you have to level up and it gets harder per ascension perk but having quest exp gain% mythstones will make it easier.
Here’s some guides for exp farming:
This guide can give you an idea of how you can level up quickly below level 50. You can ascend with or without hirlings also.
An exp farm build for after level 50 since you can be level 100 on level 50 and get level 100 gear back. You won’t lose your gear on ascension.
This is just an example meant to inspire you to make your own but it can be a nice start. Recommended to exp farm floor 101-200 if you can since they are fairly easy floors and exp gain happens to be best there. Above 200 or below 100, exp gain from enemies tends to drop and enemies become harder after floor 200 anyways. Quest Mythstone is possible on level 1 gear though.