There are no simple answers to any of these questions. It all depends on the kind of project, your experience, the budget, your investors and their requirements, etc. But what I can tell you is: don't sell yourself short and don't be intimidated into taking less than what you believe you are worth on that particular project. If the success of the film is falling squarely on your shoulders, you are worth a great deal to the project and you should be paid for that worth. We producers are human too and need financial resources to survive and thrive.
No one but you can say how much you are willing to make on a project. Sure, deals can fall through if you price yourself too high and if you are willing to let the deal fall through due to the financiers unwillingness to recognize your contributions appropriately, then again, that is your choice. If you want to take less so the film can get made then that is your choice as well. It comes down to you making choices rather than being bullied into taking a lesser deal. If you are making choices that you feel confident and comfortable with then you are in the right head space for making your deal.
It is very easy to feel intimidated by financiers and studios, especially if you are new to the business. They will prey on your weaknesses and if you show any self-doubt or low self-worth, they will jump on that and use it to their advantage. Filmmaking is a tough business in which to know your value. It is a creative field and you will find many businesspeople who don't value the creative process very high. Thus, you need to put feelers out to others like yourself and get a sense of the market value for your skills.
In the end, you need to determine how important your role on the project is to the success of the film and stand as firm as possible to what you believe you are worth. If you are worth that money, the financiers will more than likely accept your deal -- they just may not be willing to accept that reality until they have put you through the wringer.
If you are delusional about what you are worth then you need a wake-up call and work on making yourself more valuable to your projects. Just because you say you are a producer does not mean you are one. Be realistic and know your worth. I started at the bottom and have inched my way up in my expectations. You can too.
Intense negotiations are why agents and managers and entertainment lawyers exist. They know what their clients are worth and they will do the dirty work of negotiating. In my case, I usually work with my entertainment lawyer on a deal that makes sense for each project. Over time, I have come to recognize what is fair in most deals. And some day, I would like to find an agent to represent my company who can help with other deals as well.
All of this advice assumes you are a hard worker and knowledgeable of the filmmaking process and you know how to be a producer. If you tend to be all talk and no walk and have never produced a film before then you really can't demand a standard producer fee. But if you do work hard, make things happen, and you know your film would not be moving forward without your critical steps that you have made then you have every right to demand a strong deal.
Filmmaking is a business and you are working on a sellable product just as any other corporation out there. And when you compare your time to the money you make, I can guarantee your salary often falls below poverty level -- if you are even taking a salary for your efforts. Just remember, even if your deal is deferred, make sure you are getting the pay and recognition you deserve for your hard work.
Too often, producers are looked at as not really being all that valuable. And we are expected to be the first ones to give up our salaries for the good of the projects and to pick up the slack in any department, etc. But we are human too and just like the actors who demand high salaries during production, we too have bills to pay and need food to eat. So like the actors, we have value and, like their agents, we need to stand up for it!