Link Structure When Migrating From Dreamweaver

I have a large site that I created with Dreamweaver (4K pages) and I would like to convert it to WP. I just downloaded wampserver/WP and I’m going to get started working on setting everything up locally. One of my main concerns is about link structure and how it will be handled once everything is moved over. My current site is static and all of the URLs have “.html” extensions. Can I keep my folder/file structure the same when I begin re-creating all of the pages and then use permalinks to handle everything? For example, my current pages look like this:

mysite.com/article.html
mysite.com/topic1/article1.html
mysite.com/topic2/article2.html

I’m assuming the new WP pages will look like this:

mysite.com/article
mysite.com/topic1/article1
mysite.com/topic2/article2

Is there a plugin to handle this or will it need to be configured using 301 redirects or mod_rewrite to make sure all of the pages go to the correct location? I want to make sure I keep all of my link juice and SEO for the site.

Thanks!