Replacement for Avaya IP Office 500

I work for a non-profit with Avaya IP Office systems in seven locations (using PRI and POTS). We ended up buying the Avaya system because we heard that it was easy to maintain and didn’t require a lot of training for changes. I quickly found out that the updates broke more things than it fixed and that the Avaya support wasn’t all that great.

I support over a 100 people in 11 locations so I don’t have a lot of time to edit conf files for add/moves/changes. Are the add-on GUI interfaces worth using? (We are a Windows shop so I don’t have a lot of experience tweaking Linux). In Avaya Voicemail Pro I could easily see the call flows which were represented as decision boxes. Does Asterisk have something similar? Also, if someone could let me know if the following features are offered in Asterisk.

Mobile Twinning?
Reporting? (Can I tell if someone isn’t answering a hunt group call)
Hunt Group types? (Can these be setup as round robin and all phones ring at once)