What I have heard is that the active adapters always work, the passive adapters do about 75%-80% of the time. Many people consider the passive adapters a bargain, even if they're not guaranteed to work.
Thats true with the DP to DVI adapters. I've heard the passive DP to VGA adapters are more reliable. (do have that annoying blinking problem, but thats the only issue I've heard about.) The biggest issue you have is two digital screens with one analog one. Getting all three to look good together will be a chore. DHCP content probably won't work, and I'm not sure VGA has the bandwidth for the biggest screens. If you want to get started on the cheap however, its not a bad idea.