Riverfees, route and additional costs, Europe

[RogueSage]

Not sure where to put this; I've got no experience in sailing at all but I am planning to buy a sailing boat from my sisters boyfriend, then study for a Yachtmaster Coastal and sail Stockholm archipelago during the summer before taking off for bigger adventures. Ultimatley I want to get it from Stockholm to Athens through inland waterways in the cheapest way possible. I have been googling around all day to see if I can finance this trip at all but am still clueless.

What route can I take?

Is there any tolls i should be aware of?

Guest harbors, what is the standard price? Is there no cheap way out of this? (I'd love a scenario like in the swedish archipelagos where i can just sail to some uninhibited peck of an island and stay the night for free. Any solutions like that at hand?)

Is there any permits I will need?

Any other additional costs?

I dont know if this will be helpful in any way but the boat is sheriff 600 and the motor is Evinrude 4 hk. The rig is 7/8.

I realize there is a ton of things Im not thinking about due to my lack of experience, if you find yourself having the time and energy, please enlighten me.