Design

NIFT, Delhi runs a lot of short term diploma programs called CCEs. For garment manufacturers, there are some niche courses designed, one among them is about pattern making and appreciation. For production managers there may not be any specific programs but they have a lot of other courses to aid to your learning. Please check website for certificate and Diploma options related information.

You can probably pursue mechanical engineering and alongside you can pursue a machine design course.

You are already doing what needs to be done. CAD and the solid edge is enough along with interior designing.

The fee differs from institute to institute. Refer to the link below:
https://goo.gl/fNvtTd

Admission in B.Arch:
Candidates have to complete their 10+2 examination with mathematics and English as compulsory subjects & secure at least 50% marks in the examination.
Those candidates have 10+3 year Diploma in any stream, they can also apply for B.Arch programme.
Candidates can get admission in this programme through JEE Main, NATA.
Some private universities also conduct their own entrance test for admission in B.Arch such as BITSAT, SRMEEE, etc.
After completing your B.Arch course, you have a scope of higher study. You can apply for CEED and GATE.

Refer to the link below:
https://www.shiksha.com/design/communication-design/exams/nid-entrance-exam/syllabus

Refer to the link below:
https://www.shiksha.com/design/fashion-design/articles/top-design-entrance-exams-2017-conducted-in-india-blogId-11334

You can join interior design course for graduation.