Electrical – In serial communication, is the RX pin pulled high by default

You can definitely transmit data using just TX & GND.

Firstly, you want to hook up the ATtiny85 TX line to the FTDI RX line (yellow on the TTL-232R). Make sure that the USB adapter can handle 5V - I'm fairly sure even the 3.3V TTL-232R is 5V tolerant.

According to the example page for SoftwareSerial, you need to set the direction of the TX & RX lines in your setup function:

// include the SoftwareSerial library so you can use its functions:
#include <SoftwareSerial.h>

#define rxPin 2
#define txPin 3
#define ledPin 13

// set up a new serial port
SoftwareSerial mySerial =  SoftwareSerial(rxPin, txPin);
byte pinState = 0;

void setup()  {
  // define pin modes for tx, rx, led pins:
  pinMode(rxPin, INPUT);
  pinMode(txPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
  // set the data rate for the SoftwareSerial port
  mySerial.begin(9600);
}

The baudrate will be 4800 in your case. The SoftwareSerial library doesn't seem to support CTS & RTS, so just make sure you aren't using them on the host software.

Check out the reference page for more details, where they talk about some potential timing issues which may be exacerbated if you're running at 1MHz using the internal oscillator on the tiny.

To get at your question about if you can plug power directly to the pin with no resistor and have it always be high... yes, that does work.

When you have your microcontroller set to input mode you can treat the pin like there is a very large resistor inside. So using ohms law, V/R=I with V=3.3 and R=very large, lets say 10megohm gives you a current of 0.33 micro amps. The inputs are designed to act like such a high impedance so that it has a very small effect on anything externally.