Hello everyone, I'm GethN7, and for my first post, I'm going to give some advice for adding mods that change models and textures, especially anything that affect character models and textures.
1. When installing Fallout 3 and Fallout New Vegas, the first must obviously have all the original files per the latest patched version. As for FNV, I discovered it is theoretically possible to unpack all the BSAs for FNV and the installation will be successful, but DO NOT DO THIS, it will only lead to aggravation later should you do any modding, as any mods installed and uninstalled with affect the stock game files and will cause mesh and texture issues out the wazoo, so if you are tempted to unpack the BSAs for FNV for any reason, don't.
2. All mods default to Fallout New Vegas' game engine, and as explained in the other tutorial threads, the only mods from FO3 for characters or other models and textures that will work will be mesh/texture replacers, and as long as they don't overwrite any original game files from either FO3/FNV, they will work fine.
3. All FO3 mods that change meshes and textures only (no esp) will work fine, though there may be mild display anomalies if two mods that do the same thing have overlapping files overwritten. All mods that requires esps/esms must be FNV specific or converted from FO3 for use with FNV (with TTW installed)
For example:
T6M Equipment Replacer NV
http://www.nexusmods.com/newvegas/mods/45505/?
This mod will work right out the box with TTW since it uses the FNV engine by default.
T6M Equipment Replacer
http://www.nexusmods.com/fallout3/mods/17424/?
The meshes and textures not dependent on the esp will work, but the rest would have to be converted for FNV.
4. Mods that add custom hair and facial presets that worked fine with FNV should work fine with TTW. Custom Races may be an issue, especially those that have no child equivalent (especially given the default is to start FO3's storyline, where this is essential)
Note: While not recommended by the FAQ, it is possible to play as a custom race (tested with the Daughters of ARES mod) if you begin in Fallout 3. The only effects this will have is that James will default to the Caucasian bodytype and will be bald, but this will not break anything else (as of yet, has not been fully tested in all scenarios). Ghoul custom races are untested as of this point.
5. If a mod adds custom scripts to a mesh, such as mods that allow for lootable statics/activators, it may cause issues, but this can be minimized if they have a built in check for preexisting scripts to avoid conflicts. For example, this is a mod from FNV that I found quite compatible with TTW:
Ultimate Scavenger
http://www.nexusmods.com/newvegas/mods/57418/?
NOTE: Go into GECK and add the TTW ESM as a master to any mod like the above. Due to the fact the tutorial scripts will begin again if you travel via the mod provided routes between the two wastelands, this can break scripts in the process, but adding the TTW ESM as a master should prevent this.