Been Driving on manual for a while now,
I've started to doubt my driving
technique. This is currently how
I slow down:

1. Push clutch down
2. Apply brake
3. Come to a stop, or pop back
into gear
I don't touch my brake pedal
unless my clutch pedal is on
the floor. I've been doing some
reading now and it seems like
the proper method to slow
down is to apply the brake first
until you reach a low speed,
then pushing down the clutch
before coming to a complete
stop to avoid stalling.

Is my technique so bad enough
for me to change?

Or what's the proper way to use the clutch both for Engaging and disengaing gears or Stopping,
To avoid wear and tear"

I have been driving manual for some time too. I use same method as you. If you press the break first, the engine will go off.

You can just make moderation between your usual practice and what you've just read. Meanwhile,I love your usual practice of pressing the clutch first because it's much likely to change the gear.