Krita is probably one of the best free Photoshop alternatives. There's also Pixlr. That said, Photography Creative Cloud which includes Photoshop is good value if you use it a lot. Just think of the time you spend learning programs, there's so many tutorials and resources for Photoshop.
For painting onto objects directly I like 3D Coat too.
another possibility is that you accidentally clicked one of these highlighted views:
https://gyazo.com/b33e5da5b03e6bd6f881c7c08251c071
which will turn the model so that its basically invisible. try left-clicking and dragging left or right. if this is the case then the model should turn and be visible again!
This may help. It explains what bbcode is and how it's used. I'm not sure all of the functions listed on this page work with steam, but you can try! https://www.phpbb.com/community/faq.php?mode=bbcode The image related stuff is at the bottom.
Since your question is kind of broad and I have troubles understanding what you specifically want, I'll go ahead and answer it as detailed as I can. I get my 3d models from the link below and it allows me to view the 3d model in Photoshop. Note that you require the extended versions of Photoshop to view and edit 3d files. For instance, I have Photoshop Cs5 extended. link to the 3d models: https://drive.google.com/folderview?id=0BzCM739Sp68VYkdpMlFEQkdXY1U&usp=sharing&tid=0BzCM739Sp68VVnFVZ3NRQmJjeVk
After you open the downloaded examplename.psb file, you can now edit the 3d image by changing your Photoshop's window to 3d and then clicking on the button beside the (name of the gun)"_material" and opening the texture of the 3d model. Then you can download the appropriate uv chart, link below and then copy and paste this Uv chart onto the texture and then you can edit the texture and then jump to the 3d file and see the changes in real time.
Link to the Uv charts: http://cdn-01-origin.steampowered.com/apps/csgo/workshop/workbench_materials.zip
I plan to do a tutorial covering how to make skins and how to colour in the parts of the gun that doesn't get coloured by default. Such as the scope, magazine and the barrel on the AWP.
Download Blender, it's completely free and open source. You'll want to open it, exit the splash screen, press ctrl+A, then press delete. To import your weapon model of choice, click file, import, Wavefront (.obj) and then navigate to the folder with all the weapon models and import a weapon of your choice. From there, here's a great tutorial to start off with.
The pearlescent effect is controlled by two things:
That is all the control that you have over the pearlescence. If you want areas to not have the effect, these areas will have to have little or no colour, so they'd be effectively in grayscale.
From the update where pearlescent finishes were added:
> The Workshop Workbench has been updated to include this feature so you can experiment with adding this coating to a weapon finish. Using higher values will make the color bands tighter and more frequent and using negative values will flip the spectrum to start on the opposite end. It should be noted that this coating will shift the hue of your weapon finish so parts with no saturation, and therefore no hue, will have no pearlescent effect.
The pearlescent effect is controlled by two things:
That is all the control that you have over the pearlescence. If you want areas to not have the effect, these areas will have to have little or no colour, so they'd be effectively in grayscale.
From the update where pearlescent finishes were added:
> The Workshop Workbench has been updated to include this feature so you can experiment with adding this coating to a weapon finish. Using higher values will make the color bands tighter and more frequent and using negative values will flip the spectrum to start on the opposite end. It should be noted that this coating will shift the hue of your weapon finish so parts with no saturation, and therefore no hue, will have no pearlescent effect.
Substance Painter allows you to work at 4k, or theoretically at 8k if you'd like (you'd need quite the rig for that!) It's software widely used by most modern game artists, and while it's mainly for Physically Based Rendering, (which is a different shading model to what source uses) it's still very useful. It does still share a lot of features with 3D coat, such as smart masks and materials, 3D painting and so on, though I have to admity point of comparison for 3DC is perhaps a couple of years out of date. If your intended designs are more about illustration, Painter might be more than you need, but I imagine it could get the job done quite well. You can try the software out for 30 days free to see if it's what you're looking for. https://www.substance3d.com/subscribe/
When I edit skins I use Blender (https://www.blender.org/) to preview them. I've got the .obj files of all the guns and I just load them into Blender then apply my .VTF texture to it (I use a GIMP plugin to export in VTF format, I'm not sure if PS has an equivalent.) Then, whenever I make changes, I just export it to my VTF and overwrite the previous version, then go into Blender and hit the refresh button on the texture, which reloads it so I can see the small changes. It's still a bit of a pain if you work with a single monitor, but all it takes once it's set up is CTRL+E (export) then Refresh in Blender. Not quite real time, but pretty close. I was going to link the tutorial I used to learn it but I can't seem to find it, a quick google will probably give you the specifics on using Blender.