Answers

In addition to the great response above. We often have clients that complain about the flickering or the dimmer switch plate feeling hot. Those are additional reasons to make sure your bulbs are the correct type to work with a dimmer switch. The hot plate of the dimmer switch tends to be pretty common, but can be helped by having bulbs that adjust properly with the switches.

Good information above,  Most fourescant bulbs can not be dimmed without special ballast and dimmer.  The dimmer should be rated for the total watts of the bulbs used.  If using LED bulbs make sure the dimmer is rated for LED bulbs, otherwise the lights may flicker.

All good answers. It should be noted also that in incandescent bulbs there are different wattage dimmers. The most common are 600 watt and 1500 watt. The lights being controlled by the dimmer should fall under these limits. 

Yes, when using traditional incondesent bulbs make sure it is marked dimmable (most are). If you are moving into the realm of LED things get a bit more complicated. Many LED bulbs say dimmable but can only dim within a certain range. This means that when you get to the dimmer side of things you ayy notice a flicker. Often times the dimmer switch has a list of compatible bulbs.