Using Apache directives is definitely the well-known way to handle redirects. But I’m going to recommend another, easier-to-debug approach; just write your 301 Redirects in PHP using the 'template_redirect' hook provided by WordPress. The following question title links to my answer where I provide full code for solving your problem:
Just code your 301 redirects as either PHP if or select..case logic, or by using the old URL as an array key and the new URL as an array value. Performance shouldn’t be a concern because search engines will quickly adjust to the serve the new URLs and any traffic you might be receiving on the old URLs will quickly diminish.
And be sure to put your WordPress site back into its standard state of the:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress