The Secretary of State's Office has a lot of information on its website at the following address that you may want to review: http://www.sos.state.tx.us/corp/related.shtml
In addition to that you will want to organize your business into a separate legal entity such as a corporation or LLC, or at the very least register a fictitious name statement with your county recorder's office. You will also want to register with the IRS and obtain a reseller's license for sales tax. If you will be...
If you have access to the PoA document you should have it reviewed by a local attorney to determine when it takes effect. Many powers of attorney are springing, in that they only take effect once someone has been declared incompetent or incapacitated. Additionally, if you determine that it would be in your father's best interest to alter the type or scope of the power of attorney you should do this before he becomes incapacitated as it is likely that he is currently able to make changes.
Many courts have self-help clinics or clinics for low income clients. Try contacting a nearby courthouse to see if someone is available to assist with document preparation. You can also try calling the NV State Bar for a legal aid recommendation.
This question is difficult to answer without more information about the specific provisions of the contract. It seems from what you have said that they would be acting within the parameters of the contract to withdraw at least $500 for early termination but you should probably have a local attorney review the rest of the contract to determine what grounds the company had for charging you for the service and shipping.
If your contact with the other party has been classified as harassment then you should probably stop any further content with them directly. If they are being represented by a lawyer you should deal with the lawyer from now on.
I find it unlikely that defamatory statements would be taken to the police but if this person is going to seek legal action you will need an attorney to respond properly.
Your lawyer will want to see copies of all contact with the other party as well as anything...
The clause you're quoting is called a "merger clause" and states that as to the subject matter of the contract, that agreement will take precedence over other agreements between the same parties. You will probably want a local attorney to review all the relevant documents to determine exactly what is being superseded but generally that agreement between the school and your wife would only trump other agreements for the same subject matter between the school and your wife.