If there is an AEA Stage Manager working the show, I'd actually have to presume the show is Equity.....or at least ruled as a showcase, otherwise how can an Equity member work on a non-equity show? They tend to not be very forgiving of that rule.....like....ever.
My first question to you is simply: Have you been told directly that you will be taking over as the rehearsal SM? Because things said in passing are just that: Said in passing.
Deck managers aren't frequently asked to run rehearsals. They tend to not be involved in the rehearsal process until tech week. However, if your theater and this Equity theater have an agreement to share personnel then there's some leeway to be had in job titles. Flexibility and understanding go a long way in forging those new working relationships between companies. Especially if its a longer term deal.
Now if this is one of those deals where an AEA house is trying to perhaps get out of the cost of producing a whole show and bringing in another company to produce work for them.........yeah...tread a little more carefully. You aren't there to work for the AEA house, you're there as a representative of your Community Theater. Act as professionally as possible and work your tail off...It might pay off for you in spades if you catch someone's eye and they want to work with you again.
I agree with Celeste_SM....it's really hard to give any advice on pay. I've worked for $100 and a metro card, and I've worked for 1200 a week and every where in between.
Talk to your Theater's Artistic Director and see if you can't get some information about what is going on and what is expected of you. If you aren't clear about who's employ you'll be under: Ask. If you're an employee of the larger AEA theater, you may be able to expect base benefits of working for them. If you're employed as a member of the community theater, you're probably entitled to your normal stipend plus maybe a bonus for working on a larger scale. Don't quote me on it, because I'm not privy to this situation's nuances. Best of luck! Let us know how it turns out.