IELTS

You must at least bring 6.5 and 6 in each section for good chances. But, you should try to get 7 or above in overall.

You chances are high.

It's okay. My friend got in universities with GRE score of 284. So, there's no problem. But, as you are working, you should write again to get scholarships if your academics are good.

Check with the universities first and let them evaluate your profile before deciding not to take the IELTS.
There is no minimum percentage requirement. The highly ranked universities would prefer an upper first class. Normally, 60 percent is good enough to be considered for admission in different universities or colleges. You must have a good command over english so that you can be exempted from IELTS requirements.

You cannot get admission in any country to pursue MBA without the IELTS score.

Yes, you can, but if you want to study in good German Universities, you have to score 6.5 or higher in IELTS.

Yes, as most of the universities need to know your competencies in English and it becomes easier for visa interview.

I am sorry, IELTS band of 4.5 is too low. You need at least 6 band, preferably 6.5 bands minimum to pursue any course at decent university abroad. With your score, your visa will get rejected.

Dear Khurminath,
Germany is the best country for mechanical engineering but your academic grades are not at par with German universities. USA on the other hand has the maximum universities which are globally known, you can check out university options in US, Australia and UK for your studies.
Remember to study in US you must take GRE. You must also take a look at the entry requirements for all universities you wish to apply to as they differ.
Best of luck.