I guess it depends on how qualified your web-designer is. If he’s good for web design and e-commerce you should be fine. If not, it’s probably cheaper to higher a contract company to do the e-commerce/web work.
Your HR needs are really dependent on the talen of the employees.
Hope this helps!
For in-house development I would suggest the following: A seasoned DBA/Developer one who has worked in an e-commerce environment, as well seasoned Web Developer/Designer preferably someone that has worked with products such as Microsoft Commerce Server or StoreFront.
You can also check job boards such as Dice and Monster to get a general idea of the skill sets need for both positions.
I hope this helped.