I think your path will become much clearer once you have established a goal for your project. So far you have said you hope to design a robot capable of making decisions. A 555 and CdS cell can be used to fashion a robot that will decide when the sun comes up, and turn off an LED. Is that the type robot you have in mind, or are you looking for something more complex?
The first order would be to further define your objective, pinpointing the definate decision(s) to be made, and what action is to be taken. On what input will each decision be based? What mechanicals will be involved in performing the action? How much "brain power" will be necessary? Must the robot be mobile, or can its work be done in place?
Answering this type of logical thinking will clearly establish in your mind your final outcome. Then, as you think of ways to reach your objective, you will realize areas you need to master in order to accomplish each task.
Do some "brain work" yourself, and perhaps you will find an answer to most of your questions. At that point, nearly any instructional materials will be useful.
Good luck,
AllVol