Oh lord, to answer those in detail would take pages & that's why we have the Knowledge Base.
Kreelin's editor is available here & there is a turorial too iirc - if not the tut is on StreakEagle's site
yes, you can fly any AI simply by adding a cockpit plus of course there are 3rd party Migs, Sukhois etc..
Yes, I believe that we still have the latest Weap Pack although I would think that it was due an update as other weapons have been made since then - that takes time though & real life has a nasty way of intruding on gaming .
You may have to do some ini. editing to do everything that you want so I would also get the File Extractor (available here).
Then read the Knowledge Base - after that & once you've had a go if you still have specific problems post the questions.