potential activity is to increase the account without having to wait a long time, but it all depends on your posts. for example if in one week you can make 60 post, and your rank account can be instantly increased to the member, without having to wait 1.5 months
I would warn OP to make sure he makes full and constructive posts. I'm not a huge fan of buying/selling of accounts. If you do potential and spam it up to get a rank quickly there is a decent chance of ban.
I think threads like -
https://bitcointalk.org/index.php?topic=1493906.msg15033295#msg15033295 . And saying "title" in so many not asking a question in it will again lead to problems if your trying to post up to a certain rank.