Let’s try to take your points in the order you presented them.
1. Congratulations on helping to bring someone into the Church. Having done so, though, you probably do have something more than an ordinary duty to correct a misguided soul, particularly if you accepted the role of sponsor at your friend’s baptism or confirmation (see canons 872 and 892).
2. Church law recognizes something called "private vows," but these are not private religious vows (see canons 1191–1198 on private vows, as distinguished from Canons 575 and 654 on religious vows). Almost certainly, the most your friend could have would be termed canonically private, simple vows (canon 1192), which, even though they might bind an individual in conscience to perform some specific good, confer on such individuals no ecclesiastical status, authority, power, or prerogatives.
3. The right of members of the faithful to come together in groups for certain ecclesiastical purposes is recognized in several canons, notably 215, 299, and 321. But only competent ecclesiastical authority, not individual persons, can establish "institutes of consecrated life," known popularly as religious orders (canons 576 and 589). By the way, the works in which religious engage as religious are generally referred to in canon law as "apostolates," not "ministries" (see canons 673–683). Your friend’s terminology here suggests confusion on the point.
4. While it is true that every member of the faithful is bound "to work . . . so that the divine message of salvation becomes known and accepted throughout the world" and that every lay person is bound "by a special duty to imbue and perfect the order of temporal affairs with the spirit of the Gospel" (canon 225), it is also true that "they are to avoid proposing their own opinion as the teaching of the Church in questions which are open to various opinions" (canon 227). Query, therefore, whether your friend crossed the line between personally calling for the abolition (whatever that means) of Halloween and claiming that the Church is calling for the abolition of Halloween. Catholic Answers, I might add, certainly accepts the value behind canon 227 and strives to live by it.