Christian told him to shore up all of his customers, not just the two who then left.
We don't know how big the company is, just that the sales office is the original office before they expanded. It could be really big - we just don't know what service they provide. Maybe they don't need a huge office, it doesn't mean they aren't really successful (successful doesn't automatically mean physically huge).
The wining and dining is Vivian's idea for the customers, to show the human touch. They are just going to try it out on Christian first, to show him what they mean by it, and that it works. Though of course, that backfires, in a sense...