Legality depends on the tournament format -- Helpful Hunter can be legal in some formats and banned or restricted in others
For individual cards and older booster packs and boxes, you will just have to gain a lot of experience and learn the nuances of real Pokemon products and then make educated purchases, ideally with a means of recourse if it turns out you were scammed (some kind of buyer protection program, etc)
That would mean only 900 copies of each card
Not cards this time shipping supplies
A triple mind control is powerful, but it turns the entire table against you, so Nihiloors not long for the world
I can definitely see bringing out all of them, but there are also points to be made in order to keep both of them in, and even bringing in the third though this includes a more stack-based boarding plan which is a route that my list isnt able to take, as itll also force you to bring in Red Elemental Blasts