mydomain.com/wordpress will destroy the link juice. Furthermore, the word "wordpress" in slug will make the url bigger and it is said that bigger urls, complex urls are not that good. That
mydomain.com/wordpress location is only useful if you are abandoning or giving less value to your old website as a strategy, but want to keep the contents.
As it is your head, chop it in the way you want :)
I described as a detailed method : http://thecustomizewindows.com/2012/07/convert-old-html-php-website-to-wordpress-without-change-in-url/
It is the only way that keeps everything as it is, you will lick the honey of WordPress and will get no 404, no loss of backlinks.
If you are unable to perform it yourself, you can hire any freelancer from :
(1) WordPress has no control over what the charge or quality you will get from the freelancers on
jobs.wordpress.net. It is a just a reference job board. WordPress.org has no official paid service.
(2) WordPress has excellent manual : http://codex.wordpress.org/Main_Page
(3) Side by side a handbook development is in progress.
(4) There is lot of videos on http://wordpress.tv/
(5) As always there Google Search, YouTube etc. There are quite good number of helpful unofficial tutorial providing websites.