Why was it chosen to adjust difficulty every 2 weeks (rather than 2 days or every few blocks)? Is there a benefit to adjusting the difficulty every so often (ie 2 weeks) vs adjusting the difficulty every block?
Yes, there is a risk with adjusting the difficulty every block. It entirely depends on the method of adjusting. With how Bitcoin does it, if you adjusted every block, the difficulty would vary wildly due to the variance in times between blocks. However other algorithms for determining the difficulty may be able to account for that.

Adjusting every 2 weeks allows for the average time between blocks to be close to the actual time between blocks (by the law of large numbers) so that the adjustment can happen without being effected by the variance in times between blocks. The method used by Satoshi is very simple and straightforward with its effects easy to see and model.

Like almost every other "magic number" used in Bitcoin, the 2 week interval appears to simply be an arbitrary number with no real reasoning behind it.