Sorry for the dearth of posting lately. My photobucket account maxed out on bandwidth so I decided to just hold off until it reset.
Anyway, adding the hip ball to the legs it easy but you want to take a moment to ensure that the attachment points for the pistons are aligned correctly. You should make sure that these points are at the 2-6-10 o'clock postitions in relation to the tabletop if you want the torso/body of the titan level to the floor. A slight rotation (a half-an-hour or so) will give the model a sense of a little more forward motion without unbalancing the Warhound too much.
Even though the leg-to-ball socket is deep, get a pin in there anyway.
Glue the socket and the plug as well as the pin and hole. Align the pieces and assemble.
Leg assembly is complete for now. You will want to get some preliminary painting done before you look at attaching the legs and pistons to the pelvis. Next we will start work on the torso and head assemblies.