If something is suitable for a certain task then it means that using that something for that task is a good idea - for example 'An umbrella is suitable for keeping you dry in the rain.' On the other hand, a piece of paper is not suitable (or unsuitable) for that purpose. The difference between suitable and suited, and between unsuitable and unsuited is largely one of grammar rather than meaning: An umbrella is suitable for keeping a person dry in the rain. An umbrella is suited to keeping a person dry in the rain. A piece of paper is unsuitable for keeping a person dry in the rain. A piece of paper is unsuited to keeping a person dry in the rain. So... suitable and suited mean the same thing but we use the preposition 'for,' after suitable and we often use the preposition 'to,' after suited. We do not use the preposition 'to,' after suitable. The same is true for the 'unsuited,' and 'unsuitable,' pair.

Actually not so much. "He was well suited to the job". "He was a suitable candidate for the job". Maybe, suited implies a little "after the event" so it is already proven to be the case, whereas suitable is more about potential, so not yet proven. But if that difference is there, it is a very subtle one.