1) Wouldn't know, don't do BI

2) Whichever path makes sense to you. They're all valid, there's no right and wrong here. If you work a lot with 2008 and expect to work a lot in 2008 for a couple more years, maybe the 2008 cert will benefit you. If your company is moving entirely to 2012 and intends to have no 2008 server within a couple months, then perhaps the 2012 one only makes more sense. This isn't something that we can tell you want to do, it's up to what you want and what you foresee as being beneficial and useful

3) Kinda, I think that's what the people at MSL were intending.