1. What will the mod replace?
Team Forty K, as a total conversion, will replace almost everything - player models, weapons, sounds. It will feature (a) new map(s), kill icons, hud, and more. It won't change the game's mechanics.
However, due to the nature of TF2, I can't stop you from choosing what you'll be able to install. For instance, it may be possible for you to install the player models without the sounds if you choose to.
The mod will be meant to be played on the included map, but since it's impossible for me to change the game mechanics, so you won't be stopped from playing on regular tf2 maps.
2. What are the classes?
Tactical Space Marine with Bolter will take The Heavy's place.
Tactical Space Marine with Rocket Launcher will take The Soldier's place.
Apothecary will take The Medic's place.
Grey Knight Troop Marine will take The Demoman's place.
Scout Marine with Sniper rifle will take The Sniper's place.
Scout Marine will take The Scout's place.
Techmarine will take The Engineer's place.
Tactical Space Marine with Flamer will take The Pyro's place.
The Spy is still in consideration
3. Will the classes be able to wear hats?
No, all hats will be replaced by helmet addons, (visors and such) but I still won't be able to stop you from not installing those replacements.
4. Will I be able to play on regular servers?
The mod is meant to be played on the included map, however I can't stop you from using it on regular tf2 servers.
5. Is this a skin pack?
No, it will change the game fully.
6. What will be the PC requirements?
They are going to be just the same as regular Team Fortress 2. I will include LOD's, mipmaps and other things that lower the CPU usage.
7. What about the hitboxes?
The hitboxes won't be changed at all.