Do the theme is in and active? What is the 21mb file?
It is likely the wrong file you are trying to install. In your download page make sure you select ‘Installable WordPress File Only’ option and use that.
Check documentation too e.g. http://support.kreaturamedia.com/faq/4/layerslider-for-wordpress/#group-3&entry-18
You need to get permission from the author. That is more important than license.
They may allow you to for free or for a % and in general you will need the extended license too
Type wise there is not a whole lot to go on but straight off the ‘what we do’ needs to stand out and the service titles are very brash and harsh
The validation doe snot need to be perfect (and you are right most of the web is not).
According to guidelines things like forced errors from iframes etc are ok but in general if it is avoidable then it should be fixed
overall the design does not really feel premium
the whole thing needs a lot more example pages and more to it – i get its meant to be basic but still needs features and examples that justify the cost
strange width for main area? seems a bit narrow and not for any particular reason
Typography needs attention throughout
I like it BUT:
Avoidable validation issues
Typography needs attention esp. what we do and service titles
It is very like so many others on here with nothing uniquer to make it stand out
Needs more to it generally – feels a bit empty