If I theoretically extract a few embryonic stem cells from the embryo and cultured in vitro with enough nutrient to grow more cells. How many maximum of stem cells can I get? Do I need to add any compound to inhibit the differentiation progress?
Like I said in my comment stem cell culture is a very difficult process, and while people have been doing research on this for about two decades there is still a lot we don't know about stem cells. Additionally working with (human) stem cells can cause a lot of ethic problems and is therefore under strict regulations in most countries.
In principle stem cells will continue to divide until they get a signal o differentiate. In normal embryo development some cells start producing these signals at different stages, and the complete interaction of different signals allows the formation of the organism.
In cell culture one has to make sure that exactly the right signals (which are mostly growth factors) are present in the culture medium, since stem cells can easily die if they do not get any signals.
I don't have any detailed experience or knowledge in working stem cells, but a quick literature search turned up these two papers, which should provide you a good starting point. There's likely a lot more research out there you can look for.