Is it OK for me to have more than one site for my Google Adsense Account?
Yes. In fact, the more sites you have displaying Google Adsense ads, the more money you can make. You don’t even have to notify Google of the new sites. Make sure though, that any new site you add conforms to Google Adsense Program Policies, because if your account gets terminated for violating the terms of service, you won't be able to display ads on any of your other sites.
To implement ads on your new site, all you have to do is copy and paste the same ad layout code you previously applied on your original site. This is if you don't want to change the colors, ad type or channel.
How can I monitor the earnings and ctr performance between the sites?
When you have multiple sites on one account, it's better to distinguish the sites with a channel. This is so you know which site is performing better. You can monitor the performance based on the CTR%. If you need more detail monitoring in within a site, you should also create a channel for each type of ad in within a page. Create a channel with this format(SiteName-AdPosition) so you can easily analyze your reports.
The same rules apply when adding an Adsense for Search box to your new site. The same methods are applicable.