Writing and reading multiple values through serial
The simplest way is to just print them as a single line and separate them with "something". That "something" could be as simple as a space.

Serial.print(val1);
Serial.print(" ");
Serial.print(val2);
...
Serial.print(" ");
Serial.println(val20);


743 234 34 599 2 ... 427 1013 48 2 409


Then in processing you just read the entire line into a String and split it on the spaces into an array.