I can only offer some general tips at this point Hugh.
Regarding the voip.ms portal: There is a lot of information there, most of which you don't see until you have an account and log in. Creating an account is free. Take some time, hover your mouse pointer over the drop down menus and click on the question marks wherever they are found. For most users with a basic phone setup the instructions provided by DdDave should get you up and running.
If uninterrupted phone service is important to you, remember to setup a call forwarding number to a land line or a cell phone. You will have more interruptions to your phone service on voip than you had on the phone service you are used to. Servers go down occasionally, so does the internet.
When choosing a device or ip phone, choose one of the commonly used models. If you run into any problems it will be much easier to fix.
Regarding DIDs (phone numbers). If you have a number you wish to keep, start the porting process to voip.ms before you advise your current carrier; you won't risk losing it that way.
Once I get all the bugs sorted out I will post screen shots of my configuration pages along with explanations where the default settings were changed.