is it possible to send a minibot up the pyramid while it is connected with a wire to the main robot?
No, because your level is judged by the lowest point of your robot, and you cannot be in level 2 and level zero(the floor) 
We’re not sure how to post a question in the forum, so we’re going to ask it here…
Is it legal to grab onto the “hoop” at the top of the pyramid to complete your climb? I haven’t found anything in the manual specifically prohibiting it, but I felt the need to ask for a second opinion.
I believe you can
First off, welcome to the forums. To post a question, you would go here to post a general question and click “New Thread” at the top left. You’ll get a hang of the forum for other things later.
In terms of your question, what “hoop” are you asking about?
I think you may want to take a look at http://www.usfirst.org/sites/default/files/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2012_Assets/Team_User_Q%26A.pdf, as any answer you get on Chief Delphi is highly unofficial.
As far as your question, I refer you to Q&A, Q66, as a similar question. You may also want to look at Q14, same place.