Index Size, On Table, Off Table, Reindexing Online......

Hello All, Couple of questions: 1. If I have a table with 1.8GB of data how big would my ontable index be expected to be (I am assuming there is an algorithm to calculate this based on the number of columns in the index)? 2. For high performance OLTP systems, am I better placing my indexes off table or on table? 3. Why does it seem to take forever to reindex a table (not baiting here, but I thought IFX was a very performant system. Reindexing on SQL Server or Oracle seems to take much less time and can be done in an online manner, not removing my table from use??)? Any further tips you may have on idexing strategies would be welcome. Thank you all in advance, Tam.