Design of "simple" 1000W AC motor/ heating element controller
You are asking quite a few questions. I'll answer the one about calculating heat sinks and power dissipation for a triac such as the BT208. First, to determine the power dissipation refer to the datasheet. 



From the RMS current you can find the power dissipation. Since you're not doing phase control, \$\alpha\$ = 180°. So if the motor draws 4A RMS, the power dissipation will be about 5.2W maximum. Note that this says nothing about watts in the load, it's load current that makes the triac heat. 

If (and it's an important if) your mounting is the same as the quoted mounting (size of copper pad and so on) and you achieve 75°C/W then you can calculate the temperature rise. Also pay attention to figure 1 that tells you that you should not let the heatsink temperature get much beyond 100°C and the absolute maximum junction temperature of 125°C. Conservative design would keep well below those numbers even on a very hot day. So if your ambient could be 60°C inside the enclosure, and you allowed the heat sink to get to 90°C, then you could allow 30°C rise, or about 2.5W, so it's good for about 3A (with those assumptions).