I finally have the bells to go for either a Light house or Windmill. I gather you can't have both?
Nope, can't have both. But if you change your mind, you can donate another million bells and it will switch. You can do this only once however. There's no town benefit to either one so just pick whichever you think would look best.
I'm also on the hunt for the scorpion. Any strategies from those who've caught one and lived to tell about it?
What are you crazy? How about some advice from somebody who hasn't caught one: run for your life!
...But seriously, the scorpion doesn't start to chase you until you pull your net out, but it will start charging as soon as you reach for it. Have it be the only tool in your pockets, then press left or right on the d-pad to pull it out. Wait until the scorpion is a good distance away from you before you pull out the net, then wait for it to come to you and swing right before it reaches you. It can run as fast as you can so you can't run from it to try to get into a better position. You'll get only one chance. Good luck.