Thinking about picking up sewing as a hobby! Have a few Sewing Machines Parts and Sales in Los Angeles

I managed to get the use of a machine for free so I can just play around with some fabric! Will probably start with pillow cases to practice but really I want to either start making or re make some clothing!

Is it easy to re-vamp and tailor clothing that I would find at a thrift store? Or is it easier to start from scratch? What would be the best way to go about learning how to do this?

Dresses are especially to find that flatter my body type. So I’m wondering if it is easier to work off of a pattern from scratch to tailor it to myself, or get a thrift store dress that is too big and tailor it to my body?

Also, is it necessary to have one of those body mannequins? or can I get by without one while making/fixing clothes for my body type?