Conversion to Islam

No, this a matter of personal choice.

You have the choice to convert in secret, or to convert and tell them. 

What is best to do really depends on your situation and on your relationship with your parents. If you have a close relationship, and they would be hurt if you don't tell them, or if they found out by accident, it might be good to tell them sooner rather than later. If you think it would just cause problems for yourself, needlessly hurt them, or endanger you (for instance, put you at risk of being kicked out), then maybe it is better to wait.

If you think you will be living a more independent life soon (for instance, living on campus at a university, or working and living on your own), it might not hurt to wait and tell them when you have more control over your life. 

However, eventually you will (probably) have to deal with it. Although it might cause conflict and tension in the beginning, the best-case scenario to hope for is that it could eventually lead to mutual understanding. The real question here is when to go through that, and that is something you have to decide for yourself. 

Also, keep in mind that it is difficult to keep secrets, and people often sense what we are hiding or find out accidentally. 

Best of wishes on this next stage of your spiritual journey, and, yes, it is enough to have the intention to follow a marja' and to do your best to do so; you do not need to notify the marja'.

It is nice and humble to focus on service. Some people do feel called to serve communities other than their own, and I have met some people who are not Muslim who dedicated their lives to working for Muslim communities or the Islamic cause. Sometimes it is a lifelong calling, and sometimes it is a temporary calling (for instance, on a specific sociopolitical issue that one feels strongly about, or as a stepping stone to discovering one's identity or beliefs).

That being said, the psychological motivations behind dedicating one's self to service (especially to serving the "other") can be complex. There are psychologically healthy and unhealthy reasons for service. For instance, a genuine desire to help someone in need, versus the desire to feel needed. Wishing to aid those who are marginalized, versus re-living unresolved psychological trauma surrounding feelings of non-belonging. Etc.

For that reason, it doesn't hurt to look deeply at one's motivations for service to be sure it continues to be a healthy arrangement. Also, I could foresee such an arrangement eventually breaking down due to the tension of wanting to serve the Muslim community while at the same time not wanting to be part of the Muslim community, which might strike some Muslims as strange. Not everyone wants an "outsider" to help them; this may be particularly poignant today, given the legacy of European colonialism in the Muslim world, and the way some Western organizations take a paternalistic approach to Muslims and try to "save" Muslims from practices they deem backwards or uncivilized. Basically, while some people want to serve, not everyone wants to be served. 

Anyway, from an Islamic perspective, what is important is the view of Allah. That is, what is important is your relationship to the divine. What is important is the view of the divine on your religious beliefs and practices, and overall actions in life, not the overall view of Muslims or the view of Islam as a faith. 

Similarly, the core teaching of Islam is serving Allah, not serving Muslims. There are many ways to serve Allah; serving Muslims is religiously meritorious when it is done as a way of serving Allah, but it is not the only way to serve Allah.

From a historical perspective, there are some respected figures in Islamic history who were not Muslim but aided Muslims or the Islamic cause. For instance, the Christian king of Abysynnia who protected the early Muslims from persecution. If you go through the account of Karbala, you will see that a number of people who were Christian also stood up for Imam Husayn. Also in the classical era of Islamic history, Muslims and people of other faiths worked harmoniously together on scientific and other projects and also occasionally shared the same site for houses of worship. (That being said, there was more of an equal playing field in those times; there wasn't the post-colonialist or "clash of civilizations" imbalanced power dynamic.)

Overall, despite the stereotypes of Muslims being intolerant, I think most Muslims are comfortable with religious diversity because the Quran gives a place to other religions and doesn't say that all other religions are false or that all other people are doomed. Also, most Muslim cultures have historically had religious minorities. I think some Muslims also secretly like people who are different because it can get a little boring seeing the same type of people again and again. That being said, if you do work within the Muslim community, I am sure some Muslims will encourage you to convert!

Anyway, I certainly don't mean to be discouraging in any of the above; your situation is unique to your own self and surroundings; these are just some thoughts on the overall dynamics that might arise. I wish you the best in whatever paths you take in life!