I am afraid I can only answer your first question not knowing too much about the method.
If the symbol you are using means nothing to you, it is essentially worthless. However, the cross has been used for thousands of years and should never be solely associated with Christianity.
Like Jesus, the cross is a solar symbol. Therefore using an equivalent solar symbol in my opinion would be absolutly fine. Whether that be a phonecian cross, the alchemical glyph, in some traditions you could, at a stretch, even use a hexagram.
Magic should never be followed word to word, there is a basic guideline and there is room for improvisation. Magick is a science and an art- follow the guidelines but include your own personal flair.
Most of these kits show a photo of a White Crucifix candle, NOT just a cross, atleast on some sites, while others show a single normal white candle.
Most people associate a cross (like the Crucifix) as a symbol of death, human sacrifice of Jesus., iN Haiti its juju magik, a shorter cross like a Celtic one is not the same ordeal i guess.
Maybe i can make my own kit, the thing in Judaism is Minyan, a Minyan requires up to 10 males in Synagogue, most of the prayers during Shaharit (morning) Minha (mid day) Avrit (night) contain the Torah and Tenakh portions, Psalms, some of the rituels even contain what has been known as talmudic magic, although magik in Judais is doing all this with out a minyan., its why they call a jew who does not go to synagogue a bad neighbor., especially on Yom Kippur and Rosh hashanah., whatever :)
So far i find using Psalms and some and amulets to be a good source of focusing the prayer during times one has no way of if distracted or cursed, and i did find a few shofars and kabbalists who know how to make amulets with their prayers while they themselves go to mikvah to shield them from intrusive spirits.
1. The most common form of this ritual, originates from "Catholic Christian Hoodoo"--- calling for "the total and unconditional removal of the unwanted person from one's life".
Other religious, or non-religious, symbols can be substituted depending on how merciful you want to be.
2. Unless you're deep within the knowledge of Hoodoo, -NEVER-EVER-, use a mirror box during this ritual.
3. Practitioners will create a safe place, in which to practice their path. Usually, within a room which the door locks or a hidden space within a closet.
In your case, it's probably best within your bedroom or a room the children aren't allowed to enter. A locking door, is a bonus.
