I am only asking this in the forum because there is no unofficial forum and the main website is down.  My question is am I able to use REX essentials Plus OD for water textures and use REX 4 texture direct for other textures at the same time?  There are very few water textures in texture direct and there is no difference in inland water.  My rivers look like coral from the ocean.  Any suggestions?

Yes, you can!

you can freely mix textures from Direct and Essential Plus OD.

Concerning REX 4 texture direct, do you need to install the textures prior to executing FSX or can you install it once and leave  as is.  If the latter is true, can anyone recommend the best theme to download?  Thank you, guys/girls!  

you need to install textures only once, before starting the sim. Due to the infinity of combinations, I doubt there is a 'best theme'. The program allows you to download themes shared by the community, or create your own based on the current weather at your location. This feature actually works quite nicely, although I personally only change sky and cloud textures (rarely sun and water) and leave all others alone once I've found the ones which are most appropriate for the area and airport I fly from.

Thanks, Lurk; I think I'll just generate a wx theme based on ICAO every time I start FSX.