The compensation to the trustee is part of the plan payment you make every month. Under the bankruptcy code, 10% is the maximum percentage of any plan payment that can be used for Chapter 13 trustee compensation.
The monthly repayment amount is based on the amount of your debt, and how much must be paid over the next 5 years (maximum term for a 13). Thus, the amount of your trustee's fee is going to be 10% of your monthly repayment amount. So, the amount of your debt determines the trustee's fee.
As for whether to go ahead and file, that's really up to you and how you want to deal with the matter. If you want to go ahead and file for peace of mind, then that certainly can be done. BUT, if you want to hold off and see whether or not a creditor actually comes after/sues you, then you can do that as well.
The lender CANNOT file a lien against your home UNTIL after it obtains a judgment. In order to obtain a judgment, the lender must first sue you. So, if you are sued, you have at least 20-30 days to file a response; before your response is due, you can file chapter 13 and stop the lawsuit. Thus, you have time to wait and see if you're going to be sued BEFORE filing.
As for the frequency of creditors suing, it is much higher than in decades past because of the bad economy. Thus, you can expect to be sued be these credit card companies at some point. Because of that, you may just want to go ahead and file and avoid being sued, etc.
If you don't feel comfortable waiting, you should discuss that with your attorney.