Bismillah ir Rahman ar Raheem
The Yehud used to pester Musa (Peace be upon him) on every little matter - please see the case of the Ba'qara (Cow) in the Quran surah (Ch. 2: Verse 67-71) of the same name.
Thus, they had themselves to blame for a lot of limitations posed upon them, such as having to keep dairy and meat utensils separate, the Sabbath limitations, and not being able to marry anyone related to them within twelve degrees of separation.
Our Nabi (Peace be upon him) told the Sahaba not to ask unnecessary questions like the Yehud so that religion would be made easier onto them, and the Sahaba would wait for some "A'arabi" (Bedouin) new to Islam to come and ask questions (as Allah willed), so that they may learn the answers to many less than essential questions that arose in their minds - please see Bukhari's Jami al Sahih for the hadith.
Now, there are a lot of things in this world that might not be beneficial to a person maybe once in a million cases. There are also things that have small benefits but whose dangers are much more (such as 'khamar', i.e. narcotic-like substances that cloud your mind, usually translated as just 'alcohol'), or even things that have no benefits at all, and these are outright forbidden. The things that are only beneficial to us such as Salah (prayer) and Saum (fasting) are enjoined onto us and obligatory.
Now, the first kind mentioned in the above paragraph, such as mixing dairy and meat, working on the Juma'a (the real & original Sabbath) except at prayer time, and being able to marry your 1st, 2nd, 3rd.. cousin; all these are Mab'ah (allowed) for us.
On the authority of Abu Hurayrah Abdur’Rahman ibn Sakhr (may Allah be pleased with him) who said: “I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying”: “What I have forbidden you, stay away from. What I have ordered you to do, do as much of it as you can. Verily, the people before you were destroyed only because of their excessive questioning and their disagreeing with their prophets”. Reported in Bukhari and Muslim
And if among the things that are Mab'ah, anyone should face some confusion (or even if you are inclined towards one option over another) :
According to Bukhari, Volume 2, Book 21, Number 263:
Narrated Jabir bin 'Abdullah :The Prophet (Sallal Laho Alaihi Wasallam) used to teach us the way of doing Istikhara, in all matters as he taught us the Suras of the Quran. He said, "If anyone of you thinks of doing any job he should offer a two Rakat prayer other than the compulsory ones and say (after the prayer):
TRANSLATION: "O Allah! I seek goodness from Your Knowledge and with Your Power (and Might) I seek strength, and I ask from You Your Great Blessings, because You have the Power and I do not have the power. You Know everything and I do not know, and You have knowledge of the unseen. Oh Allah! If in Your Knowledge this action ------------------------------------------------ (name the action or think of it here) is better for my religion and faith, for my life and end [death], for here [in this world] and the hereafter then make it destined for me and make it easy for me and then add blessings [baraka'] in it, for me. O Allah! In Your Knowledge if this action is bad for me, bad for my religion and faith, for my life and end [death], for here [in this world] and the hereafter then turn it away from me and turn me away from it and whatever is better for me, ordain [destine] that for me and then make me satisfied with it."
Note: Related in Sahih Ahadith with slightly different phrasing as well.
So, please enjoy all the benefits and freedoms Allah has bestowed upon our Shariah (including marrying your cousins); just make sure to say Bismillah first and make Istikhara whenever you are able to.
Any mistakes herein are from me and my shaitan. Wallah o A'alan o bis Sawab (only Allah knows best).
Hifz u kum Allah