How many quality links do you need to be in the top ten of a Gaming category website?
You first have to figure out how many links your competitors have for their keywords/keyword phrase and then figure out if you can realistically compete with them for the same keywords considering your available time and budget.
Could you have one good PR'ed link and get traffic from Search Engines?
The quick answer is yes. But, there is much more to this. Just because a link has high PR, doesn't mean that it is ranked well or will drive traffic to your site.
How long does SEO take to effect one's traffic?
It really depends on your coding, keywords/keyword phrases, content development, varied anchor text, etc.
I wish there really were simple answers to your questions. SEO requires time, patience, perseverance and some type of budget.
It's not just backlinks that gets your web site to the top, although you can do that with backlinks alone. I doubt that you would get a great deal of traffic from the search engine by just getting one high PR backlink.