How soon can one manufacture a product after submitting patent application.

I join the chorus. If you mark your product "patent pending," however, be real sure that the patent claims actually cover the product that you're selling. As happens all too often, the patent claims are directed at product iteration one and then, after more r&d, the product that's actually sold is product iteration two which does not have all the elements -- or the same elements -- as stated in the patent claims.

Yes, as it is factually true. Of course, be sure not to say or imply that a patent has issued until it actually has.

Yep, have at it!

Yes. It's not only possible, but advisable to do so. Affixing the term "patent pending" or its equivalent to a product is called 'marking.' By filing an application you have the right to mark your invention and should do so to provide notice of your patent claims. Marking is also important once your patent issues, since it acts as a precondition for your ability to collect infringement damages.