Aphids are often a nuisance, they attack young shoots and on flower buds, especially during the winter months. Unless there are numerous amounts of them, they can usually be gently removed with your fingers, or killed off by spraying them with soapy water.
Orchids require regular re-potting, roughly every other year, or when the plant has filled its pot with roots and there is no room for further growth. The best time to re-pot is in the spring; using an appropriate potting mix (the ideal time is when you see the new growth starting).
Many of the tropical orchids which have been confined in greenhouses in the past will do equally well in the home on a window sill if a few basic rules are observed. The most important are ensuring that there is enough light for the plants, without too much heat, and also that there is adequate humidity in the immediate surroundings.