I'd like to try out a Mod..

[Stuie]

For RTW 1.5

The First Triumvirate v1.8
The latest version of this mod which provides different campaigns for each of the three men who led Rome during the First Triumvirate: Caesar, Pompey & Crassus

TFT v1.9 is out now:
https://forums.totalwar.org/vb/showthread.php?t=63917

One benefit of using TFT is that no vanilla files are overwritten, so you can try the mod and still play regular RTW with no messy file switchers or having to reinstall and such.

Gotta patch question...

If I am running BI do I have to patch RTW to 1.5, AND BI to 1.6. Or does the BI 1.6 patch cover both?

BI v1.6 should include RTW v1.5... but I've heard there are problems if you are using RTW Gold. To be sure, go to the options screen from the RTW menu and the version is displayed in the upper right.