Newbie questions reg. trades, buying traffic and keeping visitors

Hi all,

I've put my text MGP up about a month ago and I still have a lot to do. The most important one is getting traffic.

From what I understand, at some point I'll have to buy traffic. But, after having bought the traffic and all those visitors have seen my site, won't the traffic just drop to zero again?

I suppose that's where trades come in. After a visitor's first click, I should have a 40% or so chance the visitor's traded to one of my trades, right?

What about incoming hits from my trade partners? Should I return more than 1 hit for every incoming one? Like 130% or so is what I read somewhere.

So how does this all tie in together and makes the number of visitors GROW? I read somewhere you only need to buy traffic once to get your trades started. I don't want to have to buy traffic often.

So in summary: How does trading work exactly, and how do I grow my site starting with buying traffic once?

Thanks in advance for any replies!