One question... do I really need to use an external power source if my software will be controlling only a single servo at a time?
How are you going to power your board?
I've not read the links.... so apologies to the author if I'm repeating.... but I'd buy some sockets and make an interface board/loom. Why? Because I can then easily swap devices, which aids testing, speeds repairs etc, and if I have a faulty unit, I can return it under warranty. For testing, there is hook-up wire.
JST = Japan Solderless Terminal
You need to know the pin centres, 1mm, 1.2mm, 1.25mm etc. - check out the JST site, you will probably find specs & connector part numbers there or you may be directed to a distributor.