A Crash Course on Network Bandwidth Metrics?

Kind of Blue asks: "I work for a small software development company in India, providing development services for a company in UK. We connect to the UK client through VPN; and our correct staff strength is around 13. We are going in for a major upgrade in our internet connection — and owing to the size of the firm, cannot afford the services of a networking expert/consultant. Hence I, a layman, have been asked to look into the matter and decide on the ISP and the bandwidth. I have a vague idea about the required bandwidth — it must be around 512 kbps(remember, it's India I am talking about!) and must be a persistent connection, since we use source control softwares connecting to servers in the UK. There doesn't seem to be a 'networking for dummies' kind of resource on the web. No one seems to talk of network metrics anywhere. So, can Slashdot give me a crash course in what I need to know?" "Our present ISP gives us a DSL connection of 512 kbps on 1:4 sharing. There are frequent disconnections; and hence loss of work while code check-ins. As we are increasing in strength, I am also looking at more bandwidth. But what bamboozles me is how are these things measured? Will I get a better bandwidth if I take a 512 leased line on 1:2 sharing? When the staff doubles, should I upgrade to a 512 connection on 1:1 sharing or must I take 1 Mbps on 1:4 sharing?(There's a huge price gap between the 2 here in India) In any case, how does one decide the optimum bandwidth required for a bunch of 15 developers on VPN and Source control?"