You don't have to wash all cotton three times. I would wash denim and flannel on the hottest settings multiple times like that because they tend to shrink like crazy, but I don't typically do that for shirtings. How to treat different fabrics can be really confusing. You might want to purchase a copy of a book like Sandra Betzina's More Fabric Savvy. I believe Claire Schaeffer has a similar book.
You do need to finish your seams somehow. I rarely pink my seams--but do like to have pinking shears on hand for some things. You can zig zag over the raw edges of fabric or try one of the seam finishes shown here:
French seams are especially nice!
When in doubt, trace your patterns. Since patterns are so darned expensive, you'll be happier if you preserve the originals.
I only ever wash my fabric once before using it - I'd never heard of 3 times! I sew mainly with cottons and haven't had any trouble yet...
If you're using modern multi-size patterns, I would trace out the size you want rather than cut it. That means that if your body shape changes, you want to sew a different size for someone else or you cut and make up the size that SHOULD fit (according to the packet measurements) and find out it is too big/too small, you still have the master copy to go back to.
With one-size vintage patterns, tracing can come down to a personal choice. Some people prefer to trace so that the vintage pattern isn't damaged with pin holes. I've just started sewing 1940s patterns and have been tracing out those before I use them because the paper is a little brittle from age and I don't want to risk tearing it! If you need to make size adjustments on vintage patterns I'd trace them out. I often have to re-size patterns from the 1950s as my body dimensions don't fit the "standards". The process of getting the re-sizing right often takes multiple attempts and a lot of cutting and so tracing out the original and then cutting the traced version means when/if you get it wrong multiple times (like I do!) you haven't ruined the original.
When I first started sewing, I always cut the corner of finishing the seams. However, I definitely don't recommend that! Over time and multiple washing, most fabrics will shred and if it shreds to the seam line your garment will fall apart. Because I don't own a serger/overlocker, I zig-zag all my seams - that was a major hurdle for me because I thought it was going to add stacks of time to sewing my garment and I just couldn't be bothered. In reality, it's not that bad! I did recently buy a pair of pinking shears to use on the seams of a bodice facing where the material was particularly "shreddy".
If you only have a certain amount of fabric and are not sure if the pattern will fit well, I do recommend making a muslin. It's another super annoying process that draws out the sewing process but can be well worth it. I've only just started doing it but it has saved some of my favourite fabric and meant that the garments I make for me do fit me and I don't have to give them away!
Check out The Fashionable Stitch blog (http://www.afashionablestitch.com/2011/categories/fun-stuff-for-you...). Many of us are doing the sew along for the Ginger skirt on Sunni's blog and it addresses many of your questions.
Your latest post/blouse is beautiful by the way!
There are tons of great sewing blogs out there! Here are some of my favorite helpful posts from around the blogsphere.
Choosing a pattern size to start from:
How to work with patterns when if you are like me and the pattern says I should be using 3 different sizes (one for the bust, one for the waist and one for the hips):
Seam finishes galore:
(I'm partial to french, faux french and pinked seams.)
A dress is probably not the smartest thing for a beginner sewer, but, that said, the first garment I ever sewed was a Renaissance dress and it turned out ok. I don't usually trace modern patterns (especially if it's from one of the big three pattern companies and I know I can get it again for under $2), but now that I'm getting further into sewing, I'm thinking it's a good idea.
I am so proud of you for loosing 8 lbs..Congradulations.. It is sooooooo hard, isnt it? I too am trying my best to loose weight, and learn to eat healthy. Good luck on your diet and your new sewing..have fun and Happy Sewing.