B.A Economics

No, central scholarship is for all category.

Yes, you can get admission in economics honors without maths as well there will be a deduction of 2.5% from your overall best 4 scores. If your percentage falls in the bracket even after the deduction the college under the university guidelines is bound to give you admission.

Yes, it is. For this, the candidates should have secured at least 60% marks in aggregate in their qualifying exam. The aggregate should have been prepared by calculating marks secured by the aspirant in four subjects.

There are many courses which include economics in their curriculum. BA (Hons) Economics is one of the courses which will provide you with the specialised knowledge in economics, and it is available in many DU colleges like SRCC, Hindu, Venketeshwar, etc. You can also go for BBE, whose entrance exam JAT is conducted by DU every year. If you are looking for economics, as a subject in your curriculum and do not want to focus mainly on it, you can opt for B.Com (Hons), Maths (Hons), Stats (Hons), etc., and opt for economics as one of your subjects.

Actually, change of college depends on the university norms. As far I know it is possible only in the beginning of 2nd year, provided that your previous year's marks are good.
First, get permission from the department of your college. You should talk to your teacher in charge.

You can apply after class 12th.