They are having a big event in March which I believe they'll need me for, so this may be an issue. It's apparently in another state, so will I run into immigration problems if I fly if I don't have my EAD by March? I should have the receipt by then right? Should I not take the chance by flying? I'm assuming they check immigration status when you are boarding...right?
They don't routinely check immigration status when boarding a domestic flight; showing the DL should get you through the check-in and security lines. However, sometimes in the area where you wait to board, there are immigration agents roaming around, randomly asking about immigration status. If that happens, show your DL and I-485 receipt and you'll be OK.
I came in on an F1 visa and I have a valid DL. I have also SSN with work restrictions.
That is very good for two reasons:
1. If you find yourself forced to start work before you have the EAD, when it is I-9 time you can show your SSN card + DL + I-485 receipt. That will calm their fears about you being here illegally. Say that you're here legally with a green card in progress but now you're just waiting on your employment card which should arrive within a few weeks. That way they'll either let you suspend your working for a few weeks, or let you work while you wait for the EAD. But for that to succeed, you have to delay your start date so the EAD will arrive very soon after you start. Don't start before March.
2. You've been here with an F1, so by now presumably you are a college graduate. That means the jobs you interview for will generally have a much longer interview and recruitment process than a regular $9/hour mall job, and the amount they'll pay makes it more important to hire the best person. And the increased length of the process (multiple interviews, signoffs by HR and different levels of management to get you hired, etc.) buys more time for you.
That means once you get the offer, that gives you more leverage to delay your response, and to delay the start date. They won't want to go to the second or third-best person, and they won't want to go back to HR and other management to get approval for the next best guy. If they give you two days to reply, tell them you need a week to think about it. If they give you a week, tell them you need two. If they won't budge on giving you more time to think, tell them you can accept the job now if they'll let you start on April 1st or later. If they need you to start before that, say you'll need more time to look at your situation to determine if you can start before April (but if they give you March 15th or later, accept that).
If you didn't already negotiate a start date as I just mentioned, and you took the week or two or whatever to think over the offer, when you reply tell them you'll accept but on the condition that you start on April 1st or later. They'll ask why, and they'll probably say how come you told them you can start ASAP. Reply by saying you have some important personal things you need to take care of before you start, and they're taking longer than you want, and you want to get them out of the way before you start working, so your work won't be interrupted because of it.
But tell them that there is a possibility of completing it before April, but you can't know that ahead of time, and you'll let them know if things work out fast and you're able to start before April. They might not agree to April 1st, but by asking for April 1st they'll be more likely to agree to March 1st or March 15th. Whereas if you directly asked for March 1st they'll push you to Feb 15th.