You can pick up your ID at the registar's office. Not that big of a deal.
As a transfer, you're already familiar with normal registration process. It's not much different from other schools. Know your requirements and use the course scheduler on BU Self Service Banner, (under registration), to help layout times that work. Go to your major or school's website to learn what course sequences you need to take if you haven't already done so. From my experience, the transfer orientation people were not helpful with courses. They were only able to give advice on GenEds and the advice was not much more than, "you need a C. You should take a C." I knew more than they did and ended up helping other people because orientation staff were not knowledgable.
As for meeting people. I met tons of people during orientation - then subsequently never saw them ever again. All the transfers were from different schools and majors. At most, you'll bump heads with them walking on campus a couple times during the year when you're running to class.
** On the other hand, if you're looking for a roommate, I know a couple people that met during orientation and ended up switching rooms to live together.
Nobody mentions this, but as a transfer, you have the most leeway with courses. Talk to whomever in your respective school that deals with transfer credit. The preliminary transfer credit report is very stingy. They only gave me a handful of classes that satisfied GenEds originally. I got two more classes by just talking to the person in my school that deals with transfer credit. Then I formally appealed for another 2. I knocked out a full semester of courses just by speaking up. You already have to catch up on other courses since you transferred, no reason you should waste time taking useless GenEds