A Loooper basically acts as a true-bypass switch for your pedals. You can have more than one pedal in a Loooper's loop. You can probably get by with a single loop for starters. My rig uses a single Loooper:
bass -> loooper in -> Q-Tron -> Big Muff -> Tech 21 XXL -> looper out -> Amp
A 3-Loooper would give you a lot of flexibility and control over your pedals - for example, you could put your effects into "banks" - filters in loop 1, chorus/flangers in loop 2, distortions in loop 3 and so on, or you could isolate rarely-used really noisy pedals. There are a lot of possibilities, but it could get very complicated (and expensive!)
An A/B box lets you direct your signal between 2 different outputs or inputs - if you had 2 basses, for example.