Whoo hoooooo! Great choice, TechieGuy, you'll be glad you did.
OK, to answer your questions...
1) After you finished migrated/importing all your pages to WordPress, it's important to do a redirect so that anytime someone lands on one of your old blogger pages, they get redirected.
This site was very helpful for me.
http://laffers.net/howtos/howto-redi...r-to-wordpress
Now I must admit, my blog was not nearly as trafficked as yours when I switched so I didn't have as much of a concern about rankings. At the time I made the switch, most of my traffic to my blog was coming from my main site. Nevertheless I think that site will be of great help to you.
2) Do you have Windows? If so, follow my instructions on setting up WordPress on your PC first. This will give you a fully functional working version of WordPress on your PC. You can export your posts out of blogger and into this local version of WordPress for testing, design updates, etc.
http://blog.2createawebsite.com/2008...es-in-windows/
One tip: Before you import your posts into WordPress, make sure you select "No Archive" in your Blogger account, otherwise it will only grab the first post of every month. It took me forever to figure out why WordPress was only getting one post each month.
I think you'll be fine. I would highly recommend installing wordpress on your machine first. That way you can test everything. And the nice thing is, all your blog files are saved in one folder. So when you're ready to go live, you'll just upload that entire folder to the same area of your host.
Let us know if you have any questions. Good luck!