In the past it was easier to promote your site on YA but it has gotten harder over the past few months. Make sure your link is really relevant and don't just stick your link in there, write a good answer that will help the guy asking questions. Be careful with asking and answering your own questions with different profiles, YA catched on to this since a while.
I'm sorry but don't listen to him ... you can do this way 1 or 2 times but you sure will get banned if the mode caught you (They can see your IP and even worst, they can ban your IP too.) so don't use the cheating way. Just answer quality question and you should be fine
Yes, it isn't as easy as WebSmoker is trying to suggest here. Whenever you do stuff like this you should use a proxy or VPN and before you login with another account, change your IP with one of the 2 AND clear your browser cache+cookies (free tools like ccleaner help). For more "important" things like Paypal it's even advisable to create a new windows user before doing all of the above but I doubt it's necessary for YA. No matter which way you pick, it will always take a while before you start seeing traffic coming from YA.
yes if your answer is matched with the question then you can do it and your site must have to be matched the users requirement so just do it