I agree that setting an intial 20lb. goal is best because looking at the big picture can certainly be daunting. I remember my first WW meeting where I learned I had 130lbs. to lose. After the meeting I sat in my car and cried as I tried to come to terms with the fact I had to lose an entire person!
I found it much easier to focus on working towards achieving 5lb. and 10lb. losses (for which we received stars and ribbons at WW). Okay, so it didn't seem like a lot, but as the weeks went by my weigh-in card became filled with stars and my fridge was covered with ribbons.
I tried to stop thinking about "goal" and kept my mind on the short-term.
Mind you, after losing over 100lbs. things have pretty much slowed to a stop over the past two years and these last 20-25lbs. don't seem to want to budge, but when I think about that first meeting and remember how overwhelming and impossible it all seemed, I want to yell to everybody to always look at it as a work in progress and to remember that all those "little" losses add up in no time (next thing you know your pants are practically falling off!)
As for scales, my home ones always differed from the WW by up to 4lbs., so I tried to rely solely on the WW ones - reasoning that even if they weren't totally accurate, at least by only using one set of scales they'd always be consistant.
Exercise-wise, I started off slowly by walking nightly (an inexpensive and easy form of exercise, for sure). I worked my way from huffing and puffing for one or two blocks up to power-walking with ease for several km. Gradually I got into hiking and now I can't wait for winter to be over so the trails will be open (this from someone who used to consider "exercise" a dirty word!)
Welcome and good luck - make sure you stick around and keep posting!