In GTD-speak, a project is anything that requires two or more separate actions to complete. A context is something you need to be able to work on an action: a phone to make phone calls, Bob to discuss the design of the widget you are building together, the grocery store to buy some milk. A customer generally wouldn't be a context unless you could only work on some action with the customer present.
I'd make a folder for each product, to contain individual projects relating to that product. Projects that are sufficiently complex might be broken down into another folder full of projects (you can nest folders, of course). Nothing stopping you from having separate folders of projects for different customers.
Projects take dates just like actions. Note that the most restrictive date in the hierarchy overrules others; if you make a project that is due June 1, you can set a due date of June 10 for one of its actions, but OmniFocus will treat it as if you had set it to June 1. Similarly, if you have a project that you set to start on June 1, but the first action has a start date of June 10, nothing from that project will show up as available until June 10.
Some resource material:
http://www.omnigroup.com/ftp/pub/sof...dOmniFocus.pdf — OmniFocus/GTD white paper, aimed at the Mac version of OmniFocus, but the concepts apply to the iPad app as well.
http://www.usingomnifocus.com/resources/ — enough stuff to give you a guaranteed eye-glazing if you try to absorb it all at once!