Is it necessary to pursue B.Tech from a reputed college if I want to opt for MBA in a good college?

For career and campus placement, the reputation and placement record of college from where you have done your last degree matters the most. If you are able to do MBA from top 30 B-schools then college of your first degree has only minor difference and you will be able to have very good career prospe

No, it is not important but if you want to pursue MBA from good b-school then you should start preparing for CAT and other exams.