Hi, Mani.
You can use 80ohms for Rs. This is computed by using Ohm's law where current=31.5mA (found in the datasheet) and voltage=2.5V (your input voltage). You can also change this to a lower value depending on your test results. Just let 80ohms the maximum Rs.
AD8145 can receive any type of video format so definitely you can use this for your differential Y/C.
For the ADV7181D question, I think DaveD or GuenterL could help you more on this.
Regards,
Anna