[cHo]

once you get the wb, it will come with a bung for you to weld onto your downpipe.. you'll want to get it welded after the front and rear pipes merge to get a balanced reading of the two banks. or get 2 wb and install one on each bank.
the scanmaster 3 and hhh do the exact same thing. now the scanmaster is great because its constantly connected and lets you see o2 readings and knock sum on the fly. Which is great for constantly monitoring your car. Where the scanmaster kinda sucks is that the small screen only allows one or two things to be displayed at a time. so in order for you to get a good idea of whats going on while tuning, you'll end up doing 5-6 pulls to see each of the parameters you were trying to log. this is where something like hhh is better as you can log and see all that simultaneously. this will make tuning sessions much faster and you're not WOT your car as much. now the downside to hhh is that since you need a laptop connected to it, its kind of a pain to have a laptop in the passenger seat and hope it doesn't break if you have to suddenly brake hard or swerve. granted, if you have a bulletproof tune, then you shouldn't have to monitor it all the time but its something i like to do. the scanmaster 3 keeps it really easy to keep on eye on how your car is running and since i like to boost more than not boost, i'd like to know if my car is not running the way it should. thats why i mentioned that if you have someone local who has mmcd or hhh or any other datalogger that you can use to tune your car, just go with scanmaster to keep an eye on things.
no, the scanmaster and hhh are only dataloggers as in they log data. they cannot make any adjustments to your afr. if there are changes, its because your ecu doesn't like whats going on. you would need an afc of some sort to be able to make any changes. theres plenty of people using the maft and maft pro but as always theres haters out there. i'm not too familiar with those piggybacks but i do know that a lot of people don't think the arc2 is all that great even though matt monet used it to get into the 10s/9s/8s with it. heck.. ray pampena tuned oohnoo's car on 3si with an Apexi safc II on 680cc injectors and 19ts and made over 500awhp. now most people can't even get their car tuned on 680ccs because the lack of timing control the safc has.
to each his own, i say.. i went the aem standalone route with my suby and got it 'professionaly' tuned and blew the motor in 6 months even though i was on stock injectors and turbo and never turned up the boost past stock. not to mention a bunch of other issues the aem gave me. every single 3/s i've owned started with atleast 120k and ive gotten all of them past 180k no problem. i've been lucky enough not to experience blowing a motor or having a catastrophic failure of any sort. well.. one stealth got hit by an 18 wheeler but that had nothing to do with my tune or anything. i know there is still a lot for me to learn but all i can do is take it 1 step at a time..
good luck on your car and feel free to ask any more questions.