The above fix does work. Downloaded and installed folder 0 as per the readme, and now RDE and EUP work.
So further on from your advice AllenK, thanks!!! :
Latest GTA V Patch, possible fixes:
1. Download new GTA V patch.
2. Download new Rage Hook Plugin.
3. Download new Scripthook.
4. In OpenIV, go into 'Edit Mode' and it will prompt you on screen to upgrae your update.rpf. Do this.
5. Download and install a new gameconfig.xml file for this version of the update (until RDE, etc. provide their own fix). Try https://www.gta5-mods.com/misc/gameconfig-for-1-0944, and install 'folder 0' as per the readme instructions. This allows more vehicle and ped slots.
5. Reinstall anything that you had edited in update.rpf.
Have combined a list of advice from around the forums so thanks for those who contributed. Attempt the above to try and get crash free! Note that some call outs will not work until update by their creators.