I’m not sure what my rating is
It is 0.
i’ve ranged anywhere from 1800 to 2000 from different tests i took.
Meaningless. The only true tests are across the board from an opponent.
I do know one thing for sure, if you are playing an opponent who is rated much higher than you and you just try to defend they will line all their pieces up and tear you apart.
Very good. That is, indeed, the one thing you know about chess, and you are correct.
Try to keep your options open to castle either long or short if necessary. Don’t castle too early, see where your opponents pieces are lined up first
Nope. In the absence of a developing move that threatens something, castle as soon as possible, preferably on the kingside.
Go with moves that best fit your style
Weak players do not have a style, but they usually imagine they do. Style doesn’t manifest itself until players are master strength.
study opening moves and even practice them first
Worst advice possible. Chessplayers are as good as their ability to recognize tactical patterns at the board. Weak players can take an openings book to the board, leave it open, and consult it, and it won’t help one bit. Every move inexorably carries the players toward an ending — endgame knowledge is absolutely required because endings cannot be avoided, whereas openings can.