I think it depends on your bid.. The more you pay the more will be ur CTR.... But in terms of Conversions... adCenter is the best.... you can bid for top positions in adCenter... so that u get better conversions and CTR
Depend on your work and also ur CTR. You need to do a lots. So far, i familiar with YSM or adword only.
that doesn't make sense the more you pay the higher your ctr will be? It depends on how many keywords your impressions get vs. how many clicks you get. doesn't have anything to do with google, yahoo, or msn. to get a high ctr, having small amounts of keywords in your adgroup is a big factor so you have less keywords getting impressions. also make sure your ads are laser targetted and relevant to your keywords so you can get more clicks from people who are interested in seeing more about what they searched for.
That depends on your work. yahoo and google can give you a high ctr but it's not sure that they can give you also a high conversion.
adCenter doesn't increase the min bid even if you have a low CTR. This way you can focus more on clicks that convert.