Those Eucharistic Ministers who take Communion to the Homebound receive special training, which it sounds like you didn’t have or understand. You cannot take Communion to your Grandmother without your Priest’s permission until you take the training (which only takes about 1 hour or less) normally. Sometimes the Priest will give permission if no other Homebound Ministers are available.
To answer some of your questions in advance: Yes, you can certainly light a candle and have a Crucifix present.
You should simply wash your hands prior to giving the Communion - actually as soon as you arrive.
The Pyx (if Blessed), does not need to be “purified” – just make sure there are no remnants or pieces remaining. If any particles remain, you are to consume them yourself. You do not place the Holy Eucharist on the napkin, but take it directly from the Pyx to administer to the Recipient.
Those of us here who take Communion to the Homebound went to a store (such as Wal Mart) and purchased either a couple of large white napkins of linen or large white (men’s) hankerchiefs. Most of us prefer the white linen napkins, as they are thicker, crisp, and fold nicely. (We also fold the Pyx inside this napkin, to prevent any hard jars to the Pyx, which might break up the Host). We carry these things in a small bag (such as a plastic bag for make-up, but which is neutral or blue or black, not clear.
We also carry a small or medium plastic bottle of Holy Water (available at the nearest Catholic Gift Shop, or through the Parish, and a small glass holder for a very small amount of Holy Water. I use an antique “salt celler”, but there are small, pretty and inexpensive glass containers, about 1" wide and 1/4" deep available in the Housewares Section of Wal Mart. We wash them thoroughly before first use, then not again, unless stained. Any Holy Water left after both the Recipient of Holy Communion and yourself bless yourselves with it prior to the prayers, we usually ask the person if they have a houseplant, and pour the tiny amount left into the potted plant. Otherwise, it is poured onto the ground outside the house.
All of these things, especially anything your Parish Priest may prefer to do differently will be taught to you. Homebound Ministers are in great demand in most Parishes. Contact your Parish Priest tomorrow (perhaps before or after Sat. Vigil Mass, or your Liturgical Minister who is usually in charge of the Homebound Ministers. That person probably trained you as an Extraordinary Minister of the Eucharist.
When I had a relative in a condition of failing health and not expected to live, my Priest gave me a brief training (15 minutes) and I had the Pyx already and was allowed to take the Holy Eucharist that time to my relative. The following week I was given the Homebound Ministers training. If this is the situation, ask your Priest for permission to do so. God Bless you for wanting to help your homebound Grandmother!