1) Differentiate your product from the beginning.

Many new sellers start with RA (retail arbitrage), OA (online arbitrage) or Wholesale before to switch to PL (private label) just to find out 2 years later that they haven't actually built anything for themselves.

They didn't build a brand and don't have their own product.

Even with the PL, it's just another label on someone else's product. Very soon the market becomes overcrowded and they have to look for the next big opportunity.

You spend all that time and effort to find, source and ship the products and it's a waste.

2) Start big.

Imagine how much inventory you have to rotate if trying to scale your PL business from $1000 to $50K.
It will take a while.

Start big by crowdfunding your product modification.

Kickstarter or Indiegogo can get you to the next level in a matter of months while further testing your ideas.

3) Multichannel.

Start selling at Walmart, Sears, retail, eBay and so on instead of sourcing your next product.
It's much faster to scale your business when you already have something working, instead of trying to find your next product.
Once you've exhausted all your channel, then go add more related product to what you already sell.

I hope this helps and good luck with your startup.