Electronics Engineering

Try to get GRE score. At present Germany is providing free of education for abroad students.

Yes, you can do aerospace engineering after Diploma in electronics. You are eligible for the same.

Take up physics, chemistry and mathematics and electronics optional in 10+2. Thereafter take up engineering in electronics and communication. You need both 10+2 and entrance exam too. Or, you can do Diploma in electronics engineering and then do a job. Or you also stand a chance to use a lateral entry into second year in engineering. Other options post 10+2 is B.Sc in electronics is a good option.

You can choose to do engineering in electronics and communication at state-level colleges or IITs and NITs or BITS Pilani and other universities. Diploma in electronics and communication and even bachelors in electronics is a bright option.

 Electronics & Communication is perhaps an evergreen subject of study. Research in this field is going on for any years and I am sure it will continue for years to come. Just have no worries in this aspect. You will have plenty of job opportunities after obtaining your doctorate.

Not all colleges will offer you admission now. Try to approach local recognised engineering colleges for admission.

There are two factors that you should consider while deciding where to take admission: the stream
and institution.
If you are not very particular about the stream that you want, then go for better institution i.e. COEP. But if your interest lies strongly in mechanical and you are not getting mechanical at COEP, then you may join WEC.
All the best!

Yes, you surely can. You are eligible to pursue M.Sc after B.Tech in the same or related field.

Both have different scopes. But in my opinion you should opt for B.Tech. B.Tech is a professional degree. Jobs are more on the basis of B.Tech. Many colleges offer this course. Admission is mainly based on entrance exam.