How to read information with Modbus-RS485

In a few weeks I will receive a sensor with a modbus interface (RS485) for my work. Unfortunately I have no experience in modbus programming. I tried to document myself and I wrote this program. My arduino is used as master and the sensor as slave. I want to read at address 0x0001 the value of the water flow. In the datasheet it says: "Read out corresponding registers with function code 4 (0x04) (Read Input Registers)".
Am I on the right way or are there improvements to be made until I get the sensor back?

//#include <ArduinoRS485.h>

//#include <ArduinoModbus.h>

#include <ModbusMaster.h>

#define MAX485_DE 3   // Pin names that are connected between the MAX485 TTL to RS-485 converter module and Arduino UNO.
#define MAX485_RE_NEG 2

ModbusMaster node;                    //object node for class ModbusMaster

// preTrasnmission()  and postTrasmission() for making the Pins RE and DE of Max485 TTL to RS-485 convertor module high or low to Transmit or Receive data

void preTransmission()
  digitalWrite(MAX485_RE_NEG, 1);
  digitalWrite(MAX485_DE, 1);

void postTransmission()
  digitalWrite(MAX485_RE_NEG, 0);
  digitalWrite(MAX485_DE, 0);

void setup() {
  // put your setup code here, to run once:

  pinMode(MAX485_RE_NEG, OUTPUT);
  pinMode(MAX485_DE, OUTPUT);

  // intit receive mode

  digitalWrite(MAX485_RE_NEG, 0);
  digitalWrite(MAX485_DE, 0);


  node.begin(1, Serial);



void loop() {
  // put your main code here, to run repeatedly:

  float valueSensor;
  valueSensor = node.readInputRegisters(0x0001, 1);


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