Minimum AEA salaries range from small stipends (think $100 or so on showcases) to very large weekly salaries in the range of $2500/week. It really varies. Check out actorsequity.org and the document section for different agreements. They usually have minimum salaries for the individual contracts listed.
I'm not sure what you mean by "what do you do if you don't have a current job" --- but my best guess to answer your question: search for one! (I'm not saying that to be snide. Its the truth)
You make money weekly under AEA contracts. Some stage managers have day jobs for a while if they're working on smaller contracts, but the larger ones usually don't allow time for a day job.
Finding work in any field is always difficult. With stage management, it sometimes takes a while to get your foot in the door, and depending on your luck (really, it can come down to luck), your perseverance, and your skill, work will eventually come. It just takes time. 4 years ago I was day-jobbing it and making stipends of $250 dollars max for my work as an SM. Over time I got a fulltime SM job, then started freelancing nationwide, and now am working at a regional theatre making LORT A/B salaries. For some people the journey is quicker, for some, much longer.
These are very broad questions you ask. I can get more specific, but research on sites such as actorsequity.org, playbill.com, backstagejobs.com, and the archives of this website will probably turn up quite a few answers for you.