max they take is about 4.8V
A maximum that's "about" isn't a very useful specification!They will take it. Just don't run the Arduino and servos from the _same_ supply.
BTW I would not use the full Arduino board as a permanent installation, only for development.
I'm planning to use the arduino board as a start, both for development and simple controls like walking. I'm quite new to electronics, so that's easier atm. I was hoping to move on to something more advanced such as a raspberry pi 2 once I'm ready to program it.
I wouldn't recommend that. The Raspberry will require different software, a different software development environment, and the hardware interface will be different.
You might have to change fuse settings to keep the board running at low voltage...The problem with running arduino and motors on same power source is that the motors put a lot of electrical noise onto the power source, which can then reset the board unexpectedly...
I don't understand why people think you have to supply a 5volt Arduino (or 5volt servos) with ~5volt batteries.Why not use two (7.2volt) or three (10.8volt) LiPo cells. Or a 12volt sealed lead/acid battery.And a buck (step-down) converter.Buck converters are cheap and efficient.Use one for the servos and, if you have to, one for the Arduino.Leo..
Look e.g. here for the latest generation of low drop buck converters.Graphs included.Leo..