Salam alaikum
Your statements are partially, but not entirely true.
All Muslims, including Shia, recite 5 obligatory prayers every day. Shia have permission to say two consecutively, if their conditions require it. The three times of prayer specifically mentioned in the Quran are strictly adhered to, for the recitation of the 5 daily prayers.
There are minor differences in the wudu and salat between Sunni and Shia. There are also minor differences between the wudu and salat of various Sunni madhabs. Prostration on clay is considered by Shia to be sunnah. I've not researched this myself, but to my knowledge no Sunni school forbids prostration on earth, as there are documented hadiths recording occasions in which the Prophet (pbuh) prostrated on earth.
The hanging of pictures is a disputed issue. However, Shia who hang these pictures do not consider them to be actual pictures of their saints, but only artistic representations.
Yes, Islam is the perfect religion. Shia do not believe that they have changed it. They believe that Sunnis are the ones who changed the practice of the religion. I have not found conclusive evidence either way in my studies, and personally believe that both Sunni and Shia have changed some minor things, but the essence remains the same for all Muslims.
The massacre at Karbala is something which I would recommend all Sunnis familiarize themselves with. If some or all of the commemoration practices are wrong, that doesn't change the fact that this was a tragic occurrence in the history of the Muslim ummah, and we need to be alert that it never happens again.
Calling a Muslim not a Muslim is a very serious issue. Do you really think that determination is up to you? Wouldn't it be better left to Allah?