No Circumcision IS NOT NECESSARY for converting to Islam, For converting to Islam you should only believe following :
which means that I belivebelieve "Ali" ( Ali son of Abou Taleb, Mohammad's Cousin) is the one and only true successor of Mohammad (S).
After Converting To Islam You should start with 5 main principles (Shia's 5 Pillars) :
1.TohidTowhid ( God Is UniqeUnique -> every thing that we can think of or imagine is NOT Allah, but allah is greater than that. [it needs a little explaination...])
2.Maad (After Life, HeavonHeaven and Hell ,...)
3.NabovvatNubuwwa (Believing Mohammad (S) is Allah Messenger and...)
5.EmamatImama (believing Ali (A) Son of Abu taleb is the real successor of prophet mohammad and after EmamImam Ali, His Son EmamImam Hassan, Then EmamImam Hossein And so on... until 12'th EmamImam who is alive but hidden from the eye's, waiting for Allah permission to show him self and create a better word) ...
many people, even moslem's underestimates thiesethese 5 main principles and forget that they are pillars of islamIslam! and everything else such as:
for example, if you don't agree with each of 5 principles, you cant call your self Shia. but if you do not do one of ahkam'sAhkam's rules. then you have done a sin. but you are still a Muslim. for example every Muslim believe that he should pray 5 times each day. but he simply don't! maybe because he is lazy or... he is doing a big sin but he is still a Muslim!.
there is a famous quote from Imam Reza (A) who is Shia's 8th Imam: "Surly The Foundation Of Islam is TohidTowhid and Adl"
=> (TohidTowhid is Pillar number 1 and Adl is number 4)
circumcision is very good thing that every male Muslim is ordered to do. but if one shiaShia do not do it, he have done a sin, but he is still a Shia.
I suggest you not to think about circumcision at first place. shiaShia 5 pillars are faaaaaaaaar more important than any Ahkam like circumcision. after 5 pillars, you should start from most important Ahkam like Praying, Fasting , Taharat, ...
this is my contact email: ArmanBM@Gmail.com
If you have any question about Islam, You can just Ask it here in stackexchange.com or if it is private you can email me. I. I would be really happy :)
Fi Ammane Allah. (to be in Allah Protection)
3.(مشکاة الأنوار في غرر الأخبار، ج 1، ص 5)