[Serusers] Newbie question about multi-tenant and IVR/Asterisk Integration

Hi all, I'm relatively new to SER. I've been using Asterisk for a few years and am now trying to figure out how to move to SER and/or SER/Asterisk architecture. We offer our clients (small offices) VoIP telephony services. As such, we offer them autoattendants, IVR, voicemail, and other services common to small businesses. In Asterisk, we play with contexts in order to allow Office A to have extensions 101 thru 105 and Office B to have extensions 101 thru 110, such that when Office A dials from 101 to 103, it only rings within the Office A "space" and restricts visibility among the different offices. So, the first question I have is how to achieve this in SER? Since the only protocol we deal with is SIP, we figured we could reduce our use of Asterisk to the extreme minimal and try to do as much as we can in SER. So, probably, we would end up with Asterisk for autoattendant, IVR, and possibly voicemail as well (depending on how we can use SEMS). Now, the second question I have is. When a call comes into an office and an autoattendant answers (which is basically sort of like an IVR script), we want SER to send the call to Asterisk for the IVR script to handle it. However, when the caller makes a selection, say they press 110 to dial extension 110, we want Asterisk to send the call back to SER and tell it to transfer the caller to extension 110 and then Asterisk will stay out of the way (media). Is this possible? Can anyone provide any pointers on how to achieve these issues in SER, SER/SEMS, SER/Asterisk, and/or SER/Asterisk/SEMS? Thanks