A few things on my mind. Firstly, the issue about 170,000 polys per model - let me start by mentioning that Quake 2, with its MD2 format, could handle objects with up to 4096 triangles. But really, would you make a game with 4,000 poly models if the target PC's were from 90Mhz-500Mhz? MD5 may very well be able to handle 170k objects, but even an XP 3400+ and GF FX will chug. The models in Doom 3 currently only consist of several thousand triangles, they look much higher detail because their textures are created from models in the hundreds of thousands, and even the millions, of polys. So simply whacking in one of those high detail models could be asking for trouble if you don't take performance into consideration.
If you're going to make maps based in space, I hope they're not too populated, and I certainly hope that you don't combine space and ground scenes in the one map. Can you imagine how much memory that would eat up? That's what limits the size of each individual map - if you could fit a whole games worth of maps into your system memory, then they'd build the whole game as one continuous level. I'm not saying that the idea won't work, but it needs a lot of planning, not just building things.
Doom 3 will apparently be shipped with the level editor, like Unreal, Serious Sam, FS2 etc. Which is supposed to have a nice on-the-fly sound editor. Model converters may or may not be included, but they will come out quickly. Lightwave appears to be one of the suites used, and supposedly some of the models from the leaked alpha were in .lwo form, so that should make it easier for people to plan ahead with relevant mods.
Note that all this may change in future, so don't take my word for it.
