As the poster above mentioned, it depends.
The earning potential of your site (when it comes to Adsense) will vary greatly depending on the primary topic. A blog on personal finance will make much more money than a blog on your favorite movies. Personal finance ads pay more. So it depends on your theme.
Click through ratios depend on how your site is laid out. Do a search for "heat maps Google Adsense" and you will find some interesting information regarding where to place your Adsense ads on the page. This can make a big difference.
My CTR will range from 3% to 10% depending on the blog.
In terms of posting frequency, my sweet spot is one new post per day. I don't always hit this mark, but I find that my sites do the best when I am producing one fresh article per day.
Starting a successful forum is hard. First focus on getting that blog traffic, and then you can start pushing the forum.