Nothing I need to tell you Ragin. Nach linked a great article there and you're already clued in to Examine.com which is the best supplement site out there. Vit D is without question one of the most important supplements to take, imho. Not a supplement but actually a hormone. Any cheap version of D3 is fine. Most in North America are low. That said, get your level tested as soon as you can so you have a clue where you're at. Remember, it's fat soluble, not water soluble and can be toxic if you elevated your level ridiculously high for to long a time period. Re your question about how fast it elevates in your blood, take a look at table 1 in the first link below.
Vitamin D Deficiency Promotes Skeletal Muscle Hypersensitivity and Sensory Hyperinnervation Role of calcium and vitamin D in the treatment of muscle pain