Polytechnic

Yes, you can choose any branch in Diploma engineering. Electrical would be best because you already have the basic knowledge of it.

It depends on you. If dropping one year makes yourself sure that yes, you can take admission in a good IIT then dropping 1 year is fine but after even investing your one year if you are not getting into IIT or not getting desired job it is truly waste. So, please make yourself sure and confident that Yes, you can get into IITs.
Otherwise, your second option is also not bad. But you get less career opportunities there.
Best of luck.

You should pursue Diploma in engineering after completing ITI. You will be able to get direct admission in 2nd year.

B.Sc honors from DU University is the best option.

You will get to study basics in Diploma of engineering.

You should do diploma engineering in electrical engineering because you have basic knowledge of electrical engineering in ITI.

You can pursue B.Tech after completing Diploma in engineering in CS and IT branch.

You should not have any backlog and it will be easy for you to change the branch. You need to get a decent score in first semester.

First, you need to appear for an entrance exam conducted by the state university. Deemed universities also conduct their own entrance exam.

No, there is no branch of biotechnology. You can pursue Diploma in pharmacy and chemical engineering. But, after completing Diploma in engineering, you can pursue B.Tech in biotechnology.