Hello,
I am new on Freelancer, but have been developing in Unity for 5+ years. I have targeted both Android and iOS for the entirety of the 5+ years, and have become pretty efficient with solving issues with Unity builds.
I must say I do think the 10-15/task is a bit low, but seeing as I have yet to build a reputation on here I'm more than willing to take on jobs to get my rating up.
With that said, I do have a question regarding the chat - you say it's an asset already created? If it is an asset with simple integration then there won't be an issue, but depending on the complexity of the chat there could be more time than expected on it.
I have the latest iMac, so there won't be an issue for ensuring the app works on iOS. Ads will be a simple integration as well. I have done plenty with Facebook, but will definitely need more information regarding what you want moved around/optimized.
As long as the application is complete and looking as you wish, in addition to the chat asset being complete, I see no reason why I can't knock this out quickly for you.
Regards,
Ralph