Yes, a higher Wattage PSU is a good idea, but I would not recomend that one. You should at least get a power supply that is 80+. This is an industry standard rating system that measures the effiency of a particular power supply. The lowest award is bronze, which means that it has a minimum effiency of 80% at load. There are also silver(85%), gold(89%), and platimum(92%) awards as well. What this means is that the power supply converts the energy is draws from the wall into a usable wattage with an effiency of 80% or above. For example if the power supply is drawing 100W of power from the wall it will output 80W if it has an efficiency of 80%. A power supply with a high effiency is good, because it can save you money on electricity as it uses less power. To acheive this effiency in a power supply, it must be made from good quality parts, meaning the higher the rating, the better quality the power supply. The power supply you have chosen although having a higher wattage, does not have this 80+ rating, meaning it is a lower quality PSU. Since the power supply is what is "feeding" your computer you want to give it the best and most stable power you can. These lower quality power supplys tend to deliver unstable power, which could potentially damage your components, hence you want a good quality (and hence 80+) power supply.
I would recomend this power supply as it has the 80+ bronze rating( and hence is good quality), and has the wattage you need.
The next topic is the heatsink. Your Phenom 945 BE is what is known as an "unlocked processor", hence the "black edition" designation. What this means essentially is it can be "overclocked" to run faster than its normal stock speeds. There are two factors that influance the speed of a processor, the FSB(front side bus) speed, which is also known as the blck, and the core ratio. The 945 BE runs at a stock speed of 3Ghz or 3000Mhz. This speed is generated from a certain FSB freequency, combined with a core multiplyer. For example a FSB of 100Mhz combined with a core ratio of 30, will combine to produce an overall speed 3000Mz or 3.0Ghz (100Mhz x 30). With normal processors only the FSB speed can be changed, and usually not by much. This leads to lower overclocks as the core ratio is "locked" and cannot be changed. The 945 BE is "unlocked" meaning this ratio can be changed to acheive better overall speeds. For example 100Mhz x 40 will give a speed of 4.0 Ghz, which is significantly better than the stock speed of 3.0 Ghz. To acheive this higher speed however, more voltage needs to be applied to the processor in order to keep it stable, and running properly. This increaced voltage generates more heat meaning the processor will heat up as a higher overclock is applied. Most processors begin to physicially melt at temperatures of 90-100 Degrees celcius ( thats 194-212 farenheight). A melted precessor is good to no one. Hence the potential overclock you can achieve is highly dependant on the heatsink you are using to disipate the heat from said processor. This is why some people go to the extremes and use liquid cooling or even liquid nitrogen to acheive better overclocks. The simple fact is that with the stock AMD heatsink, you wont be able to acheive very good overclocks as it is only designed to cool the processor at its stock speeds. You will find that when you start to overclock the processor with this heatsink, you will run into wall very quickly where the heatsink just cannot cope with the amount of heat being output by the processor. The cpu will get extremely hot, and be forced to slow itslef down (which is called throttling) in order to prevent damage. If you buy a better heatsink, it will be able to more effectively dissipate the heat of the processor, which means you can acheive a higher overclock, and hence better performance.
You obviously do not have the budget for a water cooled system, so I would recomend this heatsink to you. It is very good cooler for the price
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103099 I would also watch the video as it is quite helpful.
I hope this information is useful to you, it can be quite daunting when you are getting into the PC world for the first time. If there is anything you do not quite understand, or need clarification on, please do not hesitate to ask. Myslef and fellow members of the teksynidacate formus are more than willing to guide you through every stage of process if need be.