Use the xbox controller to play alien swarm

Yes you can. You can right-click the Alien Swarm entry in your Library, click Properties, Set Launch Options and enter +asw_show_all_singleplayer_maps 1 in the textbox.

You can also do it using the console. On the main menu, open the console with ~ and enter this command: asw_show_all_singleplayer_maps 1. You might have to enable it in the keyboard settings.

Then, if you click Practice Offline, you'll get the same screen you get in creating an online game giving you access to all games.

I have no idea why they decided to do this. The AI works on every level the same as the L4D AI works. If you leave in an online match a bot takes over your character too.

By the way, another console hack: You can try using the server browser to find a game with enough open slots so you don't have to spectate. Enter openserverbrowser in the console to use it.

The easiest way would be to have it indeed as a toggle-able key. In this example I'm using F7

First, you have to go to C:\Program Files (x86)\Steam\steamapps\common\alien swarm\swarm\cfg and create an autoexec.cfg file. If it already exists, open it.

Then add these lines to the file:

sv_cheats 1
alias fps "firstperson;asw_hide_marine 1;asw_controls 0;bind F7 tps"
alias tps "thirdperson;asw_hide_marine 0;asw_controls 1;bind F7 fps"
bind F7 fps

Now you simply have to press F7 to toggle between first person and third person.

By the way, there is no skybox, so the sky will simply be very white, and you can't do hacking in the first person. You'll have to toggle back if you're a Tech.

Note: if the above path doesn't work, try replacing Program Files (x86) with Program Files.