Not a problem that you're only 16. Not a problem that you need the money, experience, and future leads. However, one thing you might not consider so much at your age is time management. You want to maximize your profit for time you spend. What I was trying to suggest is starting real small by using pre-made template or something you create that is much simpler than what you have now. Visitors to your site are going to see the website for what it is, not how much work you put in or what special tricks you were able to do.
If you were to look at the site you created versus another webpage you'll instantly recognize which was done by a beginner. For example, take these forums pages. Broken down, there really isn't much to them. A banner at the top, a logo in the top left, and some navigation tools on the top right. It's very simple, yet looks well laid out. The way you are doing your site now isn't necessarily a bad idea, I just don't think you have the artistic ability right now to pull it off.
Start small and simple. They want a page with X information. Come up with an easy layout template that only takes an hour or two to design. Then, plug in the information and let them see it. An information page like this doesn't need to be fancy and your target audience most likely knows that it's an information site about a company. You aren't necessarily trying to get new customers cold. If they are stumbling on this, they are probably in the market for some plumbing supplies. Present the information as quickly and easily as you can. The quicker the audience gets the information, the quicker they can act. Any time waiting for stuff to load, plug ins, flash, etc. is time that they have to flip back to their goggle search and try the next page (granted, something like 97% of internet users have Flash now).
Again, don't take this the wrong way. I'm trying to help you out. Like I've said, I've been in your shoes. But, the more you can produce that is nice, the better off you are. Get a simple design done and get paid. Between jobs or during breaks is when you can start tweaking and improving stuff. During your off time is when you can try and create new stuff in flash or fancy things like that. The more you can get something done, present it to your customer for feedback, and improve it is something that can help you. Dealing with the customer is often frustrating, and time consuming, and takes practice most of the time. This may very well be your father (or something like that), so if dealing with them on design and layout isn't an issue, then you're lucky. The customer is usually one of the biggest pains.
Best of luck man. You are on your way.