i've been working with buddypress for more than year and half.
i'll start with the most significant weakness i had to deal with - spammers and splogs. this is a problem you'll have to face as long as your registration form is open for everyone. i haven't found any working free plugin that can actually help you with it. you can, if you wish, pay for anti-splog plugin. i'm working with one, it's better but i still don't have a 100% solution for the problem. you can also embed google's recpatcha to the registeration form but so far i've avoided it as it's not the best solution in terms of UX.
besides of that, everything you do on buddypress - do it step by step and always remember to backup your root directory and database as things can easily go wrong. if you wish to use it on wordpress network, i suggest to install it as follows:
- install wordpress
- set it to wordpress network
- install buddypress
oh, and avoid modifing the bp-core.php as any upgrade will remove your changes (this is also true for wordpress).
feel free to ask me more specific questions if you like.