Hi Imelda,
I personally wouldn't recommend integration between WordPress and WHMCS. There are several reasons, but the most important one is related to security.
Straightforward example is that, If you WordPress blog is hacked WHMCS will be hacked, too.
You can simply install WordPress and WHMCS in separate folder, use similar layout design and operate both without "bridge" plug-in with separate databases, log-in details and usernames.
Cheers
Kal