Answer from cs61c-am (Michael Moeng 16464697) for Question 1
I am not sure how one would specifically exploit security holes, i assume it would be something like loading an integer, then using it as an address and modifying whatever was at the address.

To prevent this, one could type-tag data(000 for int, 001 for float etc.)
The tradeoff is that there are then fewer bits available to represent the data.