The only issue I see is the cannabis use, only because its only been 3 years since the use and most Agencies require a minimum of 5 years. The usage itself could be "defined" as experimental since it was 5 times in a couple of years time.
The college degree is a definate pluse. The job resignation should not be an issue, but you can expect the BI to ask you about it in depth.
As a former BI, I really don't see any issues other than what I mentioned and why.
It seems that you are already understanding how competitive LE is and what kind of candidates you will be up against. With that said, based on what you have stated you appear to be a good candidate and have a "equal" chance at LE.
My only question is, you mentioned never being arrested and the only crimes you have done are no more than misdemeanors. So what other crimes have you commited? Any thefts? Any criminal mischiefs? Did you just smoke cannabis or did you ever sell or grow any? You can see where I am going with this, the BI will have even more specific questions. And if you fail to "admit" anytging questionable it will show up in the poly and then you are an immidiate DQ, which in turn will prevent you from ANY agency hiring you!
"TO PROTECT THE SHEEP FROM THE WOLVES, YOU HAVE TO THINK AND ACT LIKE A WOLF"