Yes, that PSU is great, but op may not find one .
May get the one, like Antec VP Series 500W Power Supply (VP500P), that is good enough.
For the RAM, your MB can support ddr3 and up to 16GB. https://www.asus.com/Motherboards/P8H61M_LX_R20/specifications/
In other hand, you had the single stick memory, you want to add other one. Keep in mind, when you mix the RAM, you are better to buy the same timing and speed, also the RAM may or may not work together. Most time 8GB will be more than enough for daily usage.