Yes and no.
The 1st amendment gives citizens the right to freely and peaceably assemble. This means you are free to protest anything you would like. You can do so on public property, like the sidewalk, unless it creates some risk of safety.
In the US, any public protest is legal, as long as you apply for the appropriate permits for lawful public assembly.
They have the 1st amendment right to protest on public property, so your answer is yes. Even though they do have the right it seems as if they are not respecting the family of the fallen solider in their protest at the funeral.
It was indeed a legal protest
yes
Yes, the 1st amendment gives the freedom of speech which includes protest.
The school board can retaliate against Mr. Freeman's protest by imposing disciplinary actions such as suspension or termination, censoring his message, or taking legal action against him. They may also attempt to discredit his reputation within the school community.
I doubt it, there is bound to be some law against it.
Picket, boycott, speech.
If there is no law that makes something illegal, it is not illegal (which isn't the same thing) but for all intents and purposes, yes.
It depends how busy the road is. If it is something like a motorway, then Yes.
sue them for "conversion".
No, it is not legal to answer the door naked with an erection as it can be considered indecent exposure and is against the law in many places. It is important to respect others' boundaries and behave appropriately in public settings.