Full time Software Engineering or split time for clothing business ?

Reca,
It's admirable that you have a desire to start your own business. When I read your words, it appears that you are not too sure; I see a cluttered and confused mind probably having hard time to make a decision.
Only you alone can decide for yourself. Best thing is to ask yourself 'who do I want to be as a person long term? What kind of feelings I want to feel every day in the long term? From this you can derive the next set of questions ' who do I want to be in my life? what do I want to have and what do I want to do ? All long term questions first.
Then you ask yourself ' if I continue to work as an R & D software engineer, where will I be years from now? Will I be fulfilled with a long term career in software engineering?(If you have long term goals and visions set up in this field you might be climbing up the corporate ladder; so would that make you happy? etc etc)'
Now shift your questions to clothing business online. If I don't do this will I be fulfilled in the long term, and in short term?' What would I miss if I don't do it? What would I gain by doing this?
You have to keep asking yourself these questions that either induces pain or pleasure when you answer them.
You can even ask - Is it possible for me to start small in the short term, in a way I can manage it while I work full time? If it begins to grow, say in a year two or five, then I can always evaluate whether I want to go full time or focus part time on software,.....'
Remember the only limitations we humans have are the ones we set on our own minds
Good luck
S