You are likely to get lots of opinions on this. Here is my 2 cents worth.
As for Type, I use Polyester Thread - and as far as brand goes when I go out to purchase it now, I purchase Robison Anton thread or Sulky (I have not had good luck with Coats and Clark). When I first started I purchased a lot of 80 spools from Ebay. That thread is OK but some times I have had problems with it breaking and to tell you the truth - the finished project always looks better with the Robison Anton.
Colors are really up to you and what you plan on embroidering. If you are going to do baby stuff then an ample supply of pinks, blues and yellows might be a good place to start. Or perhaps you are going to do a mess of flowers - then choose the colors accordingly. I have not yet run out of any thread color that I purchased except for brown ( I did two stitch intensive "Moose" pillows for a gift).
I do purchase in bulk, as much as I can, bobbin thread. When you run out of it going to the local JoAnns can be expensive ( $7 - $8 a spool). I keep black and white on hand. I do not however use prewound bobbins (lots of folks swear by them but I have had problems with them).
Good luck - and before you buy in bulk make sure that you like working with it. :D