In this particular stage that you are in, while becoming acquainted with a religion, it is fundamentally important for you to put all your effort into understanding the foundations of the religion. While searching into Islam, it is not the branches or laws that you should be focusing on, but rather the very issues that define Islam.
What defines Islam is Monothesim, and that the foundation of Islam is a reason-based religion that accommodates to our intellectual and rational nature as human beings.
As for the jurisprudential matters, they are secondary matters that you look into not only through "reason", but through devotion. As you might know, Islam means to "submit" to the will and command of Almighty God, as a devout worshipper.
In the realm of Shari'ah and Islamic jurisprudence and law, there are many discussions that might exhaust you at this particular time.
However, that being said, yes, there are differences of jurispudential laws between the Sunni School of Thought and the Shia School of Thought. Furthermore, there is a difference within these schools themselves.
So, if you agree with the Sunni view on marriage, you must look into which school that is. And what is wrong with temporary marriage contracts? Should you read about it, you will understand that there are many substantial arguments that proof Mut'ah existed as a law during the time of the Prophet of Islam (s.a.w.).
In Sunni fiqh, due to the refusal of acknowledging this, they had to come up with alternatives that do not have a Shar'i basis, like misyar, and a few others.
Someone does not have to practice temporary marriage, and in reality most Shi'a do not. But, like many other laws, it is there to serve a purpose for those who require it.
As for Khums, again, what would your understanding of Khums be, so much that you "strongly disagree with it"?
If you look at religions, and sects, you will see that you are forced to give a percentage of your yearly wages and income. In Sunnism, you must give from your Zakat.
In Shi'ah law, you spend as you wish, and do as you wish, and IF you have some left over money at the end of your year, and you've placed that for savings, then you give 20% of that, not to the rich, but to support and help the Islamic community you live in.
I think this is something honourable and something we are proud of.
My advice, besides focusing on the foundations of Islam, is to stay away from being negatively influenced by bad propaganda, and look into these affairs from all angles, trying to find reliable sources as well.
With prayers for your success.