I've seen a lot of questions and discussions about build vs. buy, but most stick with the simplistic approach that you can simply do one or the other. Most of the time you have to either buy and integrate or build yourself. Either way you're in for some work.
In the next 30-60 days I NEED to implement a couple managerial projects to keep everyone from ripping their hair out and killing each other. The largest of which is a ticketing system (emails, support requests, self service, etc.).
There is no shortage of options but at the end of the day we'll have to buy whatever we decide to use, add all our clients and their users and make sure we keep things in sync over time. We'll also have to provide a single sign-on and do some design work to make it all look like we built it from scratch.
If we build we get to skip the integration pain points, albeit with a limited (but focused) feature set.
What do you typically analyze while making a decision like this? If it better to have 4-5 systems that do a very specific job well, or one monolithic system that does everything?
You've identified a key issue - when you buy you still have work to do, and potentially lots of it. Having said that my overall leaning every time is towards buy. Writing code is hard, debugging code is much harder - when you buy, you're not just buying the code/application you're buying the fact that it works - the latter is 90% of the benefit.
However, as your needs are pretty common, why not go with open source. This has two stand out benefits.
1) As you have access to the source, you can bend it to your will - ie no need to lash single sign on over the top of an existing system. Tailor the login modules to use your already existing infrastructure, therefore no need to keep things in sync, time savings, clean approach etc etc. Much open source acknowledges the real world by componentising (?) those aspects which are environement specific anyway. They're often DB/Identity agnostic.
2) If you choose wisely you will have a ready band of top tech staff who already understand the system ready to help - the only problem is they don't work for you (yet!).
My advice would be pick one of your easy targets - the ticketing system seems like the one, analyse whats out there that in the open source world that meets most/all of your needs. Evaluate and put out a request on Rent A Coder for any changes that are required. Sit back and await the results, which are hopefully excellent. You've lost a little time, and gained a lot of experience.
Open source does not equal Linux/Unix - lots of good stuff for .Net out there too.