More work will certainly follow if you treat them well. Do a good job, and make sure they know just how good your work is. Beware, though, of the big customer. Don't allow your business to become dependent on one company for most of your income. They might go broke, possibly even leaving you stuck with unpaid bills.
Big customers are important and wonderful and awful, so develop other clients as well.
Never place all of your bets on one role of the dice. I could ramble on for chapters about other small business killers like poor cashflow management, but these are all secondary to sales. Do this and you can generate a steady and appealing income. Forget it and things may be rosy for a while, but the ceiling will certainly fall in. Ignore all of the nonsense about franchises, and soak up Gerber's wisdom of designing a business for success.