Sikhism is not unapproachable. Infact sikhism is one panth which welcomes all. Sikhism says that be close to God and stay in whichever religion you are, wherever you are, Just be close to god and naam simran karo bas. Be it allah, raam or waheguru. Bas NAAM SIMRAN.
The problem is of the attitude of some people. They just forget that SIKH means a student, a disciple. So if you want to approach sikhism or want to learn something, then be a student first. As a student learn, understand the philosophy, essence of sikhism and then later on even if you want to be a critic, thats fine. But first be a student. be humble, there are prime examples in sikhism of being humble.
Well Guru Nanak Dev Ji, he is the one who started a separate sect, a separate panth and that's what is called SIKHISM. Guru Nanak gave us mool mantar. What will sikhism be without Japji saahib. So it was Guru Nanak who started sikhism and to say that he was not a sikh wont be right.Sikhism does not start after Guru Nanak or sikhism does not start with Guru Gobind Singh ji instead Sikhism started with Guru Nanak dev ji.
About saving, who the hell are we to save you. Pray to god, meditate then you can be saved and so can we. Guru de lad laggo.
About cetegories, there is only one category i.e. a gurmukh. A gurmukh can be of any religion. Gurmukh word can be found many times in SGGS, which correctly defines what gurmukh is.