Replay value?

[MisterBarca]

I had two quick questions, assuming that I won't get the "call stack function" problem with the full game:

1. I heard there are around 31 missions altogether. So how many hours does each mission take to complete?

I am a bit worried that several reviews said that the single player campaign is extremely short, which brings up the next issue.

2. I heard MP is pretty much impossible without LAN or hotseat; so you are left mainly playing v. AI when you are done with the single player campaign. I've also heard that there are no random map generators and only a map editor. So I have two questions:

a. Are there a lot of user-made maps out there?

b. If not, then is it easy to create a serviceable skirmish map?