Plugin authoring questions

I am in the process of hopefully authoring my first WP plugin. NOTE: I am using WPMU 2.7.1 (latest stable Apache, MySQL, PHP, etc. on a fresh box). Obviously I have some questions – so without further ado:

1) In actions where do_action_ref_array() is the call (instead of do_action()), can I modify the source variables passed in and have the modifications ultimately alter the caller variables?

2) Corollary: If yes to #1, is doing so forward-compatible?

3) I need to be able to add site-wide admin configurable options. How do I go about doing that? That is: How do I add configurable options? AND how do I go about differentiating between users so that only the site-wide admin can make changes…do I even need to?

4) What should a CREATE TABLE/DROP TABLE statement look like in a WPMU plugin? Also, how do I detect, preferably using WP’s provided global objects, a missing table (e.g. first-time use)?

4b) ALTERNATE: Perhaps I don’t need a new table. What sort of data can be stored in the configurable options? Full-blown PHP arrays (in particular, I need the ability to have associative hashes of associative hashes)?

5) How do I add multilingual support to my plugin? This question is low-priority for me but I can envision needing it and experience has proven that it works best to plan for multilingual support at the beginning of authoring any application that might need it in the future.