https://wiki.teamfortress.com/wiki/Help:Model_Viewer#Graphics_card_settings

This explains how to get high res for the HLMV.

As for testing, the best way to do it is to simply replace an in-game item and join a local server. I.e. you can compile your model as c_sandwich.mdl in the C:\Program Files (x86)\Steam\steamapps\common\Team Fortress 2\tf\models\weapons\c_models\c_sandwich\ folder. In-game, the sandwich will automatically be replaced with your model. Make sure to create the c_sandwich folder in your tf files if it doesn't exist.

Well first of all, a team colored sandwich replacement can be really hard to do if you are new at this stuff. First of all, you only need to apply 1 texture (the red one) to your model in Blender before exporting. The other texture will be taken care of in the QC file.

Are you also familiar with bodygroups? When the heavy eats the sandwich, it replaces the model with one that has a bite in it. So you'll need 2 models actually. As for the animation missing in-game, I don't know why that is happening. Are you using the testitem map? That feature is really bugged.

Here is a revised QC:

I've never made a sandwich replacement, so this QC might not work. I would have to test it out myself, but you can try. Make a smd called c_bananabar_bites.smd that has a bite in it. Then check in the HLMV if the bodygroup worked.

http://forums.steampowered.com/forums/showpost.php?p=34536858&postcount=2460

There is a lot to go over here. Let me answer this later today or tomorrow. Remind me.

It's always nice to hear that. Keep it up, and you'll surely get an item shipped in-game. You aren't the first person to tell me that they never had any modeling experience before watching my videos, and those very same people also have some (if not, many) items in TF2. Keep up the good work, and good luck!

Are you using photoshop or GIMP?

As the name implies, alpha channels are almost always used to control the transparency of a texture (hence "Alpha"). However, the source engine can use the alpha channel as a grayscale map for various things other than transparency (such as a phongmask, a selfillum mask, etc.). I'm assuming the transparency you are seeing is in Blender, right? If so, you can just ignore it-- this won't affect your model when you compile it in-game (btw, making weapons isn't exactly the best thing to do. Valve hardly ever adds weapons. We just got new ones, but that was the first time in a year they added weapons).

I can't recall how to disable blender from using the alpha channel as a transparency value because I never use that feature (I know that it does, but I've never seen this happen without actually activating transparency).

Weapon textures can have alpha channels. You can specify what the alpha channel will do in the .vmt file (for weapons you'll have to create the vmt manually since the in-game importer doesn't allow for weapons).

You said you wanted to use the alpha channel as a phong mask, so in your .vmt file, you should have the following lines:

You can further control this with other lines in the vmt file such as the following:

Anything black in the alpha channel will make that part of the model look dull, and anything white will appear shiny (with intermediate shininess being gray).

Are you trying to make a mod? Because if you aren't, just use the in-game compiler. I don't think the SDK works the same way anymore. I believe the folder you'll want to use for the compiler is common/Team Fortress 2/bin

Good to know. Where is GUIStudioMDL actually located, btw? Back before the in-game importer, it used to be in the SourceSDK folder, but I'm not sure anymore. Edit: Are you sure that folder works? I don't see a gameconfig file there.

It has probably changed, but try C:\Program Files (x86)\Steam\steamapps\common\SourceSDK\bin\orangebox\bin

Background images can only be displayed in orthographic mode. You'll need to go back into ortho to see it.

The alternative is to just create a plane, unwrap it, and then place your image on the plane.