It is not necessary to purchase the hosting with the same company you purchased the domain, but it's recommended (it makes your life much easier)
I don't know which company services you have bought, but I don't know any that offers templates (maybe because I'm used to design them hehe). Anyway, I know some websites that offers great quality templates at very affordable prices. One of them is Template Monster. The easiest templates to customize are the CSS ones, maybe the flash templates are more appealing but you have to know how to use Adobe Flash.
What kind of website you were thinking about? I think you should keep it simple and show off your work and a contact page (maybe an "about me" page too).
If you want, check my portfolio (it's on my profile) and I could do something similar for you (a gallery and contact page). My portfolio is best viewed with Mozilla Firefox, but with Internet Explorer is ok