c.) A person/book teaches me s.th. but afterwards i cannot make use of it right away - first have to wait further more for a new skill point to invest that on top of it all. - Why, please? Why this additional waiting period?
I think you would be by far too powerfull. They wanted a big amount of skills to give you a choice. You would be too powerfull if you had all the skills. Now you have to choose what type of player you want to be.
I think your idea would only work if they would greatly reduce the amount of skills that you could learn and spread them over the four acts. So you can only learn a couple of skills per act, otherwise you would be overpowered.
Also you don't have to spend the skillpoints you get immediately. I think it would be even wise to keep at least one skill point. So that when you reach an area which is unbeatable, you could select the proper skill that would make life easier.