Here is a good thread discussing IQ S-Line vs PowerG:
You can mix and match, no need to go all one or the other. PowerG is great for the extra range and I would recommend it if budget allows.
Indoor Siren ??? — What options do I have?
The PG9901 would be recommended.
Garage Door Sensor ??? — Can I use a window sensor? I have Liftmaster IQ
IQ Tilt sensors are commonly used. The Liftmaster garage cannot be used as an alarm sensor, but you can set up notifications based on its status, which may be all that you need depending on your intention.