How many hours a Scrum Master dedicate to a project?

Personally I think you are putting too much thought into this.  And trying to come up with a formula is very much like trying to come up with a project plan to deliver something in 12 months. Those plans are rarely correct and not useful.

As you said there are a lot of factors and they change daily, sometimes hourly.  Much like the development team will forecast a body of work to be done during a Sprint and then adapt their work on a daily basis so should a Scrum Master.  You never know how much time is going to be needed in facilitating the removal of impediments or discussing with a Sales Manager how their interactions with the team are being detrimental.  Your formula can give you an estimate but I caution against using it as a rule.  

I have worked with up to 5 teams at the same time but each of those teams were at different levels of maturity and there were times where I was allocating almost all of my time/energy on a single team.  I eventually gave up a couple of those teams to another Scrum Master because 2 of the 5 teams were going through some difficult times due to changes Product direction or team make up.  

If you are a new Scrum Master I would not even consider taking on more than 1 team in the beginning especially if the teams are new as well. You may have the knowledge needed but experience is what you should gain before attempting to take on additional teams. And if the team is established the action of introducing a new Scrum Master could cause impact to the dynamic.  Don't rush things.  Learn how to be effective with a single team before you attempt to forge the way with multiple teams. 

Being new to Scrum and thinking your biggest concern is how many teams a Scrum Master can help may be your first mistake.  In my opinion the hardest part of being a Scrum Master is being an effective servant-leader and getting the organization to recognize your ability to provide value in the role. Again, that is my opinion and you may have already been able to accomplish that in your organization.  You didn't elaborate on where your organization is on the Scrum journey so it may be easier for you than the organizations I've dealt with. 

Welcome to the world of Scrum and good luck. I encourage to visit here often.  There are a lot of people here that have great opinions, experience and techniques.  And all of us like to share because it makes us better. I learn things every time I come.  Hope to see your name a lot more.

Let's say we work 160hs/month when full time, so this Scrum Master can manage 5-6 Projects maximum.

Why do you think a Scrum Master ought to manage a project at all?

Am i going the right direction on my thoughts?

Suppose you considered each Sprint to be a project, and the project management function as being devolved across self-organizing & cross-functional team members. Might that influence the direction your thoughts are going in?