Welcome home, this is exciting and a veritable white tornado of Grace is heading toward your family, the results will be earth shaking but the best thing that ever happened to you.
Unless your catechist specifically assigns a certain dress just wear what you normally do to church, standard business attire (not business casual) is always appropriate. It is not necessary for a baby to wear white, but just a tradition, the parish usually gives you the token white garment as part of the rite.
a good rule of thumb for a sacramental donation made directly to the priest or deacon–which is always just that, never a fee–is an amount comparable to an hourly fee any professional would charge in your area. You can adjust up or down depending on your means. You may also make a donation directly to the parish if you wish, but for a wedding or convalidation they probably have a set fee for use of the church and hall.
Bear in mind the average cost of conferring a sacrament including the preparation classes and resources, misc. costs such as candles, white garment and other materials is at least $25 per family (it can be much higher in some places) and that does not include overhead for salaries or the operation of the parish plant. So that might be a helpful guideline for a sacramental donation to the parish. Bear in mind while priests have a modest salary they appreciate donations (on which they pay tax if they keep) or which some put toward charitable giving or parish needs. But deacons are often not salaried and the only recompense they receive for their services are donations. So if you intend the donation to go to the minister, put it in an envelope with his name on it.
This may be more info than you need, but I am anticipating your thread will inspire more questions.