Agree with the general consensus: men and boys serving at the altar are fulfilling clerical roles, so they should wear cassock and surplice (choir dress).
They are
not acting in the roles of higher orders (e.g. reading the Epistle or Gospel, etc, mimicking a deacon, etc.), and so they should not wear vestments.
An alb is a vestment.
They are also not religiously professed, and so they should not wear anything like a habit.
Obvious exception: if you ARE religiously professed, your habit is part of your choir dress, so wear it with joy

.