You really need a local criminal attorney who regularly practices in Federal Court. It sounds like you are undeniably guilty. It sounds like your only hope for winning the case with a non-negotiated plea is a Successful 4th Amendment Suppression motion. A local attorney is going to know, regardless of the law, how the particular judge assigned is going to look at that motion and what your chances are. A proffer may potentially get you a significantly reduced plea deal. Depending on your exposure under the Federal Sentencing Guidelines, this could be a significant difference.
Motions to suppress evidence are never a sure thing. Even an experienced federal defense attorney cannot reliably predict the outcome of a motion to suppress evidence in federal court. There are too many variables involved in the litigation of such a motion to ever be 100% sure of the outcome. But an experienced federal defense attorney will be in the best position to give you an idea of your chances and, importantly, the risks and potential benefits.
You need experienced federal defense counsel immediately. If you cannot afford to pay an attorney, you should contact the federal defender's office in your area. Often, they will appoint counsel for someone who has received a proffer letter or target letter.
To answer your question more directly: can you proffer and then fight the case through a motion to suppress? Yes, that is theoretically possible. Theoretically. In my experience, most proffer agreements provide you some protection: the government agrees not to use your statements directly against you. But most proffer agreements allow the government to use your statements at a proffer against you if you make a statement inconsistent with your proffer or even take a position in litigation that is inconsistent with your proffer. (I haven't seen your proposed proffer agreement, so, obviously, I don't know how it is worded.)
Bottom line: proffering before litigating a motion to suppress could be fatal to your motion. Proffering could undermine your motion entirely. You need experienced defense counsel to help you make this critical decision.
Think of it this way: having a good understanding of a medical condition doesn't qualify you to decide is a major surgery is a good idea or not. You need the doctor's help in making that decision. The litigation involved in a suppression motion is major surgery in the legal system. A lot can go wrong, and it is best to have expert advice before making a decision.
My answer to your question is based on the facts that you provide in your question. Additional factual details about your situation could change my answer completely. The law in inherently uncertain and always subject to change.
I saw in your comment to Mr. Fazio that you have an attorney. I'm pretty sure your attorney will explain to you that, by accepting the proffer "deal," you'll be waiving all defenses, including your chances to suppress evidence. You can't have your cake and eat it, too, and you can either fight the prosecution or work with them. Still, all proffer deals are different, so explore your options with your lawyer.
The contents of this answer should be considered friendly advice, not legal advice (I'm a pretty friendly guy), and the answer should not be construed to constitute an attorney-client relationship. If you'd like actual legal advice, call me for a free consultation at 813-635-0222. Also, if you liked this answer as much as my big ego thinks you did, be sure to click the thumbs-up button!
This is precisely the time an astute federal criminal practitioner can learn about the case against you, evaluate the defenses, and evaluate the options and compromises inherent in providing a proffer in exchange for something the value of which is speculative. You need someone whose legal opinion is one you can trust, and who can effectively negotiate with the government on your behalf.
There are many fine federal criminal court lawyers in Jacksonville. I suggest you consult with several before you make a decision like that on your own. Good luck.
The above is provided for educational purposes only and is not legal advice nor makes you a client of the Mosca Law Firm, PA. Please consult with a lawyer in order to obtain confidential legal advice that is tailored to your specific situation and facts.