>A) How can arrests occur prior to removing the corruption from the DOJ & FBI?

They can't.

>B) How can arrests occur prior to safely securing a majority in the SUPREME COURT [CONSTITUTION - RULE OF LAW]

Here Q is expressing, outside of public unrest-inducing martial law and military tribunals/coup, their only option is to secure a supreme court majority.

>C) What is the role of the SENATE?

The Senate essentially regulates the house, and approves POTUS actions.