Q1 - Yes you can keep using Mobil1, its a good oil too and CeraTec can be used with all commercial motor oils.
Q2 - If you want to choose LM, then you have SynthOil High Tec Fully Synthetic Oil in 5W40.
In both above cases, changing oil at 5K kms is wasting money. Atleast make it to 8K kms. Or switch to LM SynthOil and drain oil after 12K kms with a change of oil filter in the middle.
Do flush your engine with the LM Engine Flush to get it clean, this way the new oil can perform even better. You should use flush at every 3-4th oil change.
Q3 - Yes they really work. And in regions like Pakistan where fuel quality is really pathetic, it is a much needed product. They helps in cleaning the fuel system, injections, cumbustion chamber, as well as protects the reservoir and other parts from corrosion. Plus it also upgrades the RON of the fuel and gives better combustion.
An internally clean fuel system will definitely give you better performance. And a good combustion will give good power. Both combining gives lesser pollutants and are kind to the environment.
I hope it clarifies.