Thank you for making a post clarifying what you are saying.
All I can say is that most of your issues are actually covered in the FAQ on the Tales of Two Wastelands site. Fallout 3 mods need to be converted to the new vegas file formats and shit
Here's a method for doing this
Converting FO3 mods for TTW is no longer as easy as just changing the master, but its still pretty simple.
Download the most recent FNVEdit (3.0.29 as of this post) and also download the attached ConversionPack.zip. Unzip the conversion pack into the same folder as FNVEdit.
Load TTW and the mod to be converted into FNVEdit (this is now MUCH faster)
Right-click on the mod to be converted, choose Add Masters... and FNV, FNV DLCs, FO3, and FO3 DLCs.
DO NOT ADD THE PRE-ORDER/COURIER'S STASH PACKS UNLESS YOUR MOD REQUIRES THEM, THEY ARE NOW OPTIONAL.
Right-click on the mod again and choose sort masters.
Expand the mod and click on "File Header"
Click on the empty space DIRECTLY ABOVE 'Fallout3.esm', hold down the control key and press the down arrow until Fallout3.esm is AFTER GunRunnersArsenal.esm and BEFORE Anchorage.esm.
Save and quit FNVEdit
Reload TTW and your mod to be converted into FNVEdit
Right click on your mod, choose Apply Script, and choose 'TTW Conversion Script'
This can take a while to run. Running it on Fallout3.esm takes 90 minutes. Running it on BrokenSteel.esm takes 4 minutes. Just be patient.
All done, save and quit FNVEdit.
This means the mod is CONVERTED for TTW, but it does NOT mean the mod has been UPDATED for TTW. For example, mods that place .32 ammo will NOT have that ammo removed, you must do that manually.
New Vegas mods almost all work with few problems, because the New Vegas files aren't getting changed much.
Most people experience performance improvements, particularly in Fallout 3 with this mod. Which makes sense, they're updating the Fallout 3 files to New Vegas files. Like I understand your concerns, but just a few minutes perusing the FAQ at the TTWL website I linked answers these questions for the most part.
FAQ | Tale of Two Wastelands
General Questions
What is Tale of Two Wastelands (TTW)?
How do I travel between wastelands?
Why do I have to patch the files myself?
Is TTW available in other languages?
Can I load a Fallout 3 save game?
Crash or no menu at startup!
Crash when starting a new game!
Installer gives file not found error!
Mods and Modding
How do I install mods for Fallout New Vegas? <-
How do I use Fallout New Vegas mods with TTW? <-
Are there TTW-specific mods and compatibility patches? <-
How do I use Fallout 3 mods with TTW? <-
How do I use body and armor replacers with TTW?
How do I use weather and lighting mods with TTW?
How do I use companion mods with TTW?
How do I increase the level cap past 50?
How do I get started making my own mods and helping with TTW? <-
Disclaimer
Of course, its a mod, things won't go 100% but this mod has had a lot of time and effort put into it by people who've been trying to make this happen since New Vegas released. Their first attempt got shut down because of the legal issues bethesda's lawyers have with the project, hence they installer and the requirement that the games be legitimately purchased copies for the process to work.
Note that Gamebryo's flexibility is why this is possible. There's even a port of Morrowind's game files into Oblivion and I think maybe Skyrim now. Yep. Google Morrowblivion for the Morrowind to Oblivion engine conversion.
http://www.gameinformer.com/b/news/a...im-engine.aspx
Oh and Project Nevada is totally compatible, except don't use the weapons mod because it will duplicate all the guns, basically.
If you use Project Nevada, please do not use the Equipment Module, as you will get duplicate weapons and ammo (PN Equipment adds the original Fallout 3 weapons to the game). Otherwise, Project Nevada is compatible with TTW.
I personally don't see a lot of value in using FONV's engine to play FO3 and it seems like a high risk modification.
This is actually not true, at all. In fact updating Fallout 3's files to run in New Vegas converts them to a more updated version of Gamebryo and thus makes them more stable. I'm not a tech and mods geek so I can't explain this as well as a programmer, but basically, all Bethesda games run on Gamebryo. Importing map and other files from one to another is a relatively simple process. So actually your initial impressions are founded in a lack of awareness of this fact. I hope you'll consider this and look into it more because this is actually one of the more painless (broadly speaking) modifications to the game files one can do.
Also, a lot of Fallout crashes aret due to utilizing low memory amounts. If you download a 4gb .exe that helps address this issue. But I wasn't using one while playing with TTWL and had no issues with crashes at all. Rock solid.
Here's a link to a 4gb .exe
4GB Fallout New Vegas at Fallout New Vegas - mods and community