Finalizing SSL installation (WordPress)

We have SSL certificate installed on our WordPress site (we use InMotion hosting). Now we'd need help from a WordPress wizard to modify current .htaccess file so that SSL (https) is forced making sure the site works properly and nothing gets broken, all old links will work etc. This should include also:
- cleaning .htaccess file if there's something there shouldn't be (just adding the SSL forcing code won't do the trick)
- update WordPress to use SSL (You can find information on changing your SiteURL and Home in our Support Center at ---------- ; You may also need to use a plugin such as SSL Insecure Content Fixer to update all of your links to load over HTTPS. You can find this plugin at ---------- )
- Once you are ready to enable HSTS you will be able to do that by modifying your .htaccess. You can find information on doing that at ----------
- setting 301 redirects (so that no old links will be broken, this is extremely important)

You would need to be experienced and careful because we cannot afford any downtime and the old links should work immediately. This should be a very small task for an experienced developer. We will provide credentials to our InMotion CPanel, of course.

After everything works smoothly under https, we'd need a little optimization for WordPress itself to make it work faster. We will provide more info about the optimization later, as a separate project. At first, please just give us your price for the SSL project.

If everything goes smoothly, we have also other potential projects in mind with other sites.