Hi,
Thank you very much for your valuable question and I am very glad to know that you are trying to create a question answer Website.  It is very important website because a lot of people will get Useful information from this website.

And you have select the correct theme for your website. Because this theme is very easy to use and install. And you will all features of a ideal Q&A website (See demo from official website). You can see more details from here.  but I will suggest you to buy this theme from there official website  because you will get support 12 month free support.

You should not download and use free theme because

* You will get many unnecessary script on your theme which is very bad for your website.
* This unnecessary script may damage or hacked your  website.
* You must find some script provided by the author of that website from where you will download.

So I will suggest you that do not download and use free theme if you want to run your website safely.

On the other hand, if you buy theme, you will get this following facilities –

* You will not get any unnecessary script on your theme.
* There is no footer credit
* You will get 12 months support from the wordpress expert theme expert (You can get extra support if you need).
* This thing will be 100% safe for your website because there is no hacking script or unnecessary script on your theme.

I will suggest you to download QAEngine 2.0.14 from Engine theme official website and use safely.

So Download download QAEngine 2.0.14 – Question and Answer WordPress theme 

Thanks again for your question.