Hey, Eric; pipes for the pipe clamps would be the best place to start. You'll need 'em!
-Glue alone, if done properly should be more than just OK.
-Better would be splines in the butt joints; you wouldn't need to run the slots right to the ends if you didn't want to see the splines when it's finished.
-Doing it in sections or all at once is really your choice, but as you suggested, being able to run the glued components through the planer before the final glue up might be really helpful.
It's going to reduce the amount of time spent surfacing the finished assembly substantially!
You'll probably get as many opinions as there are active members, but in the end it'll be your choices and really that's the fun of woodworking. None of the choices you proposed are wrong or potentially disastrous.
But in the end, yeh, you need the pipe clamps...or a huge work bench which would allow you to use wedges and cauls to clamp the perimeter.
(You might find Titebond II easier to use than the III...but again, there's no right or wrong on that.)