I don't know about the satin, if I used I'd probably try shiny side in. If you think you might want to use it for backs, then you should try it however you would actually use it. I'd be afraid of skipped stitches and other things that would be more the fabric than you, I think you would get many different results by changing your thread/needle combination with satin.
For pure practice I recommend sheets from the thrift store. Cotton always best, but low blends almost as good. You can follow the patterns on printed ones, you can draw patterns or use rulers or stencils or whatever other techniques. Cheap, plentiful, pretty much guilt free.
Thread practice should be brands you want or are planning to use. Same with needles. Go ahead and spend the money and use the threads. I try to buy in bulk/on sale.