I think you would be ok with leaving your last job if you can justify why you did it to the satisfaction of your interviews. Also if you show you've been productive during your time away from work it may show as a positive thing rather than a negative. A bit like taking a gap year I suppose. Having your own business can also impress a prospective employer again as long as you can justify why you no longer want to be self employed.
I don't think many people are able to start working in infosec straight away I think most learn their trade as techs and sysadmins. I work in Infosec but I'm not nearly as much on the techinical side as many here. I work mostly on policy, procedure and auditing to make sure the tech are working as securely as they tell me they are. I work within legistalive frameworks so you may also need to remember that you will need to learn some of the legal aspecs of infosec.

As for the weed... if you are going to get tested stop early. Cannabis residue is one of hardest to get out of your system and can be found in your hair up to six months after your last smoke. It also hangs about in your blood for over a month.
In addition if you have any family predisposition to mental disorders such as schizophrenia and depression in greatly increases the likelyhood of these developing.

Alchohol is more dangerous but it's socially acceptable to be drunk but not stoned.