Download Steam Splash Creator from http://www.crazymoocow.net/ load your image, and pressm make splash. Place the tgas created in /half-life/your mod dir/resource/background and it should work.
It is possible, you could make a lot of scripted sequences and triggers, like one for every inch and make the G-man walk to the triggered scripted sequence. That would make it look like Gman follows the player.
I don't know if this would work in practice tough.
You have set an invalid path in on of the breakable glass things. It's the one closest to the door. Change the spawn on break path to: models/headcrab.mdl And i don't k now about those other models, they look weird