Excellent news on the import.
Can you go to the forum admin > Integration > Page and permalink. Make sure the correct WP page is showing at the top (it probably is) but change and update it if not. Then click on the update forum permalink button and try loading some pages. More than one.
If still only loading the front page we will need to look at what other plugins you may have active. Ie., do you have a redirection plugin or the Yoast WP SEO plugin?
On the registration front – have you actually opened up your WP site to accept registrations? – WP admin menu > Settings > General.