It is important that your website be an authentic representation of your farm. Don't over reach yourself and try to make the site fancier than you need or have more components than you can keep up with. Just be yourself. Your customers want to hear your story.
Promote your website
No one will go to your website if they don't know it is there. There are a number of local directories where you can list your website. Buy Fresh Buy Local and Local Harvest are two main ones that your customers go to search for local farms. It can be really useful to put a footer in your email that points people to your site. You can also do some really innovative things to promote your site. For example Plough Share Farm did a sweepstake on their facebook where they gave away one free CSA share to one of the people that signed up for their newsletter. This gave them access to a long mailing list they can use for advertising in the future.
Make your "About Us" page a quick snapshot of the farm
You want this page to tell someone who knows nothing about the farm who you are and what the farm does succinctly. You may want to have a history of the farm somewhere on the site. But it does not go here. Make "about us" to the point and remember your audience.
Keep your navigation clean
Your navigation needs to be the same on each page. Where do you want people to go most? Do you want people to buy your products online, join the CSA, or come to an event? Use keywords like "FAQs", "contact", and "about" to direct people to the right pages.
Keep it fresh
In order to keep your site up to date, you want to make it easy to update. If you have to pay someone each time you want to update, updates will happen less often. To make sure updating happens, make a schedule or assign one person on the farm to the updates.
Websites are always a work in progress
It is nice to have a relatively filled out site when you make it live. But remember you can always update the site. There will always be things you did not know you needed at first.
Your story is interesting - Keep in mind, people want to hear what is happening on the farm. Most people work in an office. What might seem mundane to you - i.e. fixing irrigation pipe, is interesting to them.