TOEFL

The TOEFL IBT test measures your ability to use and understand English at the university level. And, it evaluates how well you combine your listening, reading, speaking and writing skills to perform academic tasks. Mostly TOEFL is accepted in USA, Canada and IELTS are mostly accepted in the UK.
While the TOEFL only tests academic subjects, the IELTS' academic option will have academic reading and writing sections combined with general listening and speaking sections. Both, the GRE and the GMAT have an Analytical Writing Section, but the GRE has two tasks instead of one (as is the case with GMAT).

Yes, you can give IELTS only. Almost all the universities in Germany ask for IELTS. It is European based and TOEFL is American based.

The right time to start preparing for GRE & TOEFL is actually from the pre final year of your course. Because it helps you to practice more and do good at the time of examination. Also, most of the admission process in foreign universities will start right after the completion of your final academic year. So, you will not get time to prepare for the exam if u start late than this time.

Qualifying to work in New Zealand just got easier. Immigration New Zealand just announced that starting November 21, 2016, you can submit TOEFL iBT score to prove English-language proficiency for the Skilled Migration Category. To qualify for a skilled migration visa, applicants will need to obtain a total score of 79 or greater on the TOEFL test. Applicants can use their score from a TOEFL test they sat for within the last 2 years of the date they submit their application. For more information, please visit the immigration New Zealand website.

Hi Bhushan,
GRE requirements vary, it is mainly required to study in US. If you are planning for a Masters in US then yes you must take the GRE alongwith your TOEFL or IELTS test. Check university websites for admission requirements, it differs from campus to campus.

Hi,
You need not take both. Either one will suffice. I will recommend IELTS, more preferred in Europe on the whole.

You can give any one. Both are accepted. But if you are applying to an SPP college then IELTS is preferred.

Hi Pratiksha,
Yes you can. Most of the applicants do a self study. There are plenty of resources online such as online test prep materials, practice test modules etc. Take practice tests, it is the best way to understand your areas of improvement. Some of the best books for GRE include
The Official Guide to the GRE by ETS, Manhattan Series and Barron's GRE Practice Tests. For TOEFL you can check The Official guide to the TOEFL by ETS and Kaplan TOEFL iBT Premier.

You have already been told that GMAT is compulsory by another expert. Understand that for MBA abroad rules are the same. For TOEFL preparation check: ets.org/toefl