the game being closed and no one being able to join it sounds like a port problem, which is one of the biggest problems our game has when it comes to getting new players. Maybe tupac or evil~ryu on the forums can help you out there.
You can have computer bots in online games yes, though you cannot choose if there on a team or against each other, so no 2v2v2 or anything like that, it would end up a 2v4 instead. or a free for all if you choose the free for all settings.
As for advice, if you plan on playing with other players, if you get asked "s9?" from a player upon joining a Garden of War game, answer 30k or they will ban you from there game. They do this because they don't want noobs in there game. if they ask you "11?" answer 65k. Our community is a bit shit to newer players so if you're not just playing with your friend you'll have to endure a bit. The custom maps community is a bit more open to newer players, but can still be harsh.
If you're wondering what s9? means it's a location on the map with a gold mine where if a clock was pointing at 9'o'clock it would be pointing at this mine in question. When you are asked "s9?" they are trying to ask you how much gold does the mine in Small-9 contain. The answer is 30000 gold, 30k for short.
with "11?" question, same thing. The mine if a clock was pointing at 11 o clock, this contains 65000 gold.
Hope that helps if you ever play Garden of War and encounter these type of questions from other players.
Watching games is also a nice way to figure out how where to build your buildings in certain spawn locations, if you build it in the exact spots you can sometimes wall your base off or shorten entry points for your opponent. if your playing against computers, a wall-in like this with a Cannon Tower or Catapult is very helpful compared to just making alot of towers everywhere. As they would need to destroy your farms, barracks, lumber mills or whatever you placed in the wall-in spot first before they can reach your tower/catapult. This is good because the other buildings have alot more health then a tower, and you can always repair your buildings with peasants/peons when they're attacked too.
hope this little bit of advice helps