1. If there is no proof that Pashupathi is Shiva, there is no proof as well that it is not Shiva..
2. Before Rigveda was compiled it was oral, It was passed from generation to next generation. The teaching of vedas was not confined to planes, Even southern Indians too learnt it. The Vedas is not made/formed by one rishi, It is knowledge (Research) of many rishis (from all over India).
3. Swastika can be Indian origin, Only because it is found in other culture as well We cannot say it is not Indian. Lol, Gaytri Mantra is part of Rigveda and OM is mentioned here.. Facepalm
4. Yes Aethism/Nature-worship/ monoethism/polyethism etc, all are part of Hinduism. Hinduism is amalgamation of many such ism.. Boudh, Jains are considered as Hindu and we Hindu have all kind of relation with Baudh, Jains, Sikhs (including marriage)
5. Lol! Hinduism as religion may be 5000 year old, but Hinduism as culture, society, thought process is 15000 to 30000 year old..