I'm glad Reth is getting some fans! :D
Qrom you have the chance to see naked under the following conditions:
- Got a ride from Silas in the beginning
- Flirt with him (requires charisma 14+)
- Have earned at least 3 affection points with him (arm, belly and chest will get you enough points)
- Then you'll get to the scene where you have the option to see him naked
To see Silas naked you need to meet the following:
- Have told him the truth
- Have earned 15 or more affection points with him
- Then you will have an option to tell him about your dream and either knock or just walk into his room
Also, yes. There are plans to have a customization function for the main character's appearance, but that is going to be much further down the road. So at the moment it's just his silhouetted side face.