In July it will be 5years that I will have been a father. My son and I have a good relationship. I am a very cultured man and I really respect and appreciate the privacy of people. Sometimes whenever I want to hop in to the bathroom or change my clothing, my son also wants to bath with me or see my nudity, is it normal to allow your son to see your private parts as a father? Is there anything wrong with such an act?
At that stage nudity has no special meaning for children. They are comfortable running around naked all day (weather permitting) and they don't think anything about other people being naked or not.
That's actually a pretty healthy thing to happen: the more they understand "that's how a human body looks like" and "they come in all forms of shapes, sizes, and colors", the less susceptible they will be to body image issues later in life.
So go ahead, be as naked as you comfortable with: it's not going to hurt the kid in any way form or shape.
At some point you will have to deal with your environment. Many cultures and most religions have strong tabus around this and they hopelessly entangle nudity and sexuality. This depends highly on your local circumstances, so I don't think there is one-size-fits-all approach.
A simple example: Just about that age going out with my daughter became complicated. She was too young to go to the bathroom on her own (especially in a place she didn't know), but too old to be acceptable in a US men's room and I certainly wasn't allowed in the girls room. So pee-breaks became always a major ordeal and some malls actually provided "family bathrooms" to help with this specific issue.
To my knowledge and experience, when a child of that age sees someone nude, they literally just see someone without clothes on, without any further connotation to it. Their main curiosity will be about what the human body looks like and how their body looks like or differs from the other one's body.
I have a son of a similar age who sees both me and my wife regularly nude. We are comfortable with that, so we only put light boundaries on it. For example, her occasionally takes a bath with either of us, without anyone wearing a swimsuit. But, I am not comfortable with someone watching me when I use the toilet, so that is where I put my boundary. On the other hand, I sleep nude and when my son calls out in the night, I don't bother to put something on. I attend to him as I am.
You have to put your boundaries where you are comfortable with them and those boundaries may/will shift as your child grows.