The ideas you have are lovely!
You could have 3x church candles in different sizes grouped in the middle of the centrepiece and then have lovely foliages such as spruce, ivy, salal and something varigated (the two tone pale green/cream foliages) and add some roses and eryngium(thistle) etc around it. Not sure if you are doing these yourself?
I suppose other flowers you use will depend on availability and colour scheme/taste.....lisianthus is lovely and wax flower....
You will need a flat dish and green oasis big enough to sit the candles on and still have room for the flowers etc.
If the flowers are kept in a cool place they can be stored/transported and will be ok for a few days( eryngium and foliages last for ages!)
Stunning Wedding and Event Flowers in Yorkshire