1: It does appear you need to switch cds to use the different campaigns, but i've been too caught up playing BI to try yet.

2: The 1.3 patch is only for people who have RTW installed, if you have RTW and BI installed your RTW is already updated.

3: No patch out for BI yet, the 1.3 patch was just bringing RTW up to the same patch/adding multiplayer compatibility with BI RTW.

4: You'd have to talk to player1 or someone using the mod to be sure, but I think the patches are seperate for each campaign. So just install the BI bugfixer if you want to use it for BI.