I have started one business with three distinct product lines while working a full time position.
I do have two pieces of advice based on my 6 months so far;
1; take a win as a win, don`t fret about it because it wasn`t exactly what you thought, at the end of the day you will learn more.
I started selling a product that I thought was a sure fire winner, ended up selling a ton of a product a customer asked for that I didn`t make, and only sold a few of the original product. Lesson ? listen to the customer.
2; take a win as a win, don`t burn yourself out trying to grow faster than you can grow. Making the biggest selling item takes a few hours, promising more product than there is time to manufacture will kill you and compromise everything you do. after a near breakdown, I take the orders with the understanding they may not get it immediately, most will wait, some move on, all are gratefull of the honesty.
I say go for it, structure it so you can handle it, and keep the day job until your business can support you completely for a long time to come.