Struggle between exploration and boundaries

mrsoc

I am not looking for any advice really, just discussion. 

This age is so hard to sort out what to let him do to explore and what to do to set boundaries.  This has to do with what to let him climb, playing with his food and drink, toys in his mouth, etc...  DH and I are always trying to figure out where to draw the line, as I do not want to always being saying no to everything (which I try to limit) and he needs to figure some things out, but I also do not want to have him doing things that later on may be a problem as far as behavior.  

Again, where is the handbook??