Many people say, "Oh, you need to do 15|10 at the VERY LEAST," but most of those people are hypocrites. Do whatever time control you want, but IMO rapid is the best for learning, it doesn't need to be long, just 10 minutes.
This is so true, most of my improvement came from 5|0 blitz games.
#1
"What books should I read as a 400 rated player in order for me to improve?"
++ None at all. A low rating of 400 is a sign that you often blunder. Think carefully about every move and check that your intended move is no blunder before you play it. That alone should get you to 1500. Hang no pieces, hang no pawns. Whenever your opponent hangs a piece or a pawn, take it.
Join Coaching until atleast you learn all of the basics. It will approx take 2-3 months to learn all basics of chess. then you can start solving mate in 1-2 puzzles.
#1
"What books should I read as a 400 rated player in order for me to improve?"
++ None at all. A low rating of 400 is a sign that you often blunder. Think carefully about every move and check that your intended move is no blunder before you play it. That alone should get you to 1500. Hang no pieces, hang no pawns. Whenever your opponent hangs a piece or a pawn, take it.
That won't get you to 1500 alone, not hanging pieces.
You need a little positional knowledge, and tactics.
#1
"What books should I read as a 400 rated player in order for me to improve?"
++ None at all. A low rating of 400 is a sign that you often blunder. Think carefully about every move and check that your intended move is no blunder before you play it. That alone should get you to 1500. Hang no pieces, hang no pawns. Whenever your opponent hangs a piece or a pawn, take it.
That won't get you to 1500 alone, not hanging pieces.
You need a little positional knowledge, and tactics.
tactics=not hanging pieces and taking hanging pieces=tilt... for me at least 
I hung a knight in a rapid game (moving too fast) but when my opponent took it I trapped their queen. It was on purpose, for sure...
There is no need in books at that rating to get better, just practice everyday. By practice, i mean solving puzzles, playing games and analyzing your mistakes. It is just a matter of time and effort for you to climb up, serious stuff like books are for professionals.