If at 59 1/2 I withdraw from my 401K, can I do it once and leave the rest of the money in my account or do I have to take more payments?

You can make as many (or as few) withdrawals as you want, whenever you want. The one exception is if you had previously elected for what is known as a 72(t) withdrawal - typically this is a technique used by people less than 59-1/2 to avoid paying an early withdrawal penalty. To qualify for the exemption from the penalty under these rules you are required to take essentially equal withdrawals annually.