The best way to determine how much to charge is to figure out what your goal income for the year is, add in your expenses then divide by 52 to figure out what you need to make each week to make that number. Decide how many shoots you feel you would like to do during a given week. Next, divide your expenses by the number of shoots. That will get you in the ballpark. If you feel the number you come up with isn't feasible then you need where you are able to compromise to get that number in line.
As a photographer, I agree with what a lot of what Flagship Photo said for rights. Realtors will pay for shoots (yes they often compromise and use cell phone photos etc) but it is your job to convince them of the value. Typically you will find a handful of high-producing realtors that understand the value and will pay, and a lot of realtors that aren't big producers that are hesitant or outright refuse to pay. Often times the less producing realtors will follow the big producers lead eventually but not always.
In my experience Realtors are not too keen on having to worry about copywrites and such. I would go so far as to say they disregard any concerns the majority of the time. Remember they are your customers, so you have to find a compromise that will give them what they want but pay you what you deserve, or decide not to work with them. Many photographers work up an agreement giving the Realtor rights to use the images pretty much however they would like, but you will want to be sure you retain ownership and the right to use for your portfolio.
The biggest complaint I hear is a photographer doing work for Realtor A, then when Realtor A loses the listing Realtor B just takes the images and uses them. Obviously, that doesn't quite seem fair to the photographer.
You will have to inform the Realtors of your policies up front, let your clients know the policies prior to the shoot and then pick your battles when it comes to protecting your rights. You can fight for the principle of the matter but you might find yourself without clients pretty quickly.
I am confident that won't sit well with many photographers and ultimately it is up to you. I will say clients who understand the value you bring will be the most willing to pay fairly for your work and are typically willing to work within your parameters. The clients who consistently try to talk you down on price are more likely to complain and be difficult to work with.
I hope that helps.