1. No, you cannot add monsters into CS. The only monster I know that is allowed in CS is monster_scientist, and that's not even an actual monster, that's a hostage. However, if you are willing to download some Metamod plugin named Monster by botman (I think that exists), then it is possible.
2. If you mean you didn't go up to them and press your "USE" key and they don't follow you, then why dont you try that next time?
If not, then blame the hostage following code, I guess.
But the hostages do not have to have a path defined to follow you.
3. You posted in the wrong forum. This is the Map and Mods section, where people show off their maps and their Mods. I think you're looking for the HL1 Mapping Questions forum. That one is the first when you enter the list of forums.