Hi,
Not really a great coder myself, but I am building a smaller site as kind of hobby project, trying to incorporate all the best practices of RWD. My first approach as my skills in CSS & HTML were quite limited was to buy a template on Themeforest. I noticed very soon however, that modifying these templates is quite difficult to do, and it's even harder to understand exactly what each element in the css is used for (there was no documentation inside the css)
When I ran some checks with external tools, I noticed that for all the templates only 30% of the css was actually used. Load times were pretty mediocre, mainly because the huge number of external javascripts used for all the fancy stuff on the page. Maybe I bought the wrong template, but my general impression is that these templates are developed based on frameworks which are already quite bloated (Bootstrap, Foundation) - and then they add a lot of additional jquery plugins for things like sliders, responsive menus, ...etc.
If you just need a temporary fix - you could try one of these templates - they are cheap & functional, even if they do not fit your needs for 100%. For the final version, it's probably better/cheaper to find a great designer/coder to build your code from scratch rather (or based on a very light css framework) than to clean the code in the template.
rgds,
Dirk