Hi there! I will do my best to answer each question with what my experience has been....take it for what it is worth.
1. We are using cloud only Office365 for email and apps, though Lync is a hybrid installation.
2. We have a mix of E4, E3 and email only licenses....running a little over 200 total right now with probably 70% E4.
3. Yes, we have the retention enabled.
4. Have not yet needed a real-world search but we did do some in test during early deployment. Process was fairly painless and seemed reliable. We've only been on O365 for about 4 months...
5. We had an issue with this last month. A problem on the servers at MS led to a half-day's confusion around here because we didn't know the problem was on their side until after wasting a fair amount of time troubleshooting local settings on the scanners, relays, etc. MS was a little slow in acknowledging the problem and propagating communication during the event. I voiced my concerns in their feedback section but never heard anything more. Their status portal has great potential but you are still subject to when they decide to announce the degradation in service. Having administered the backend servers myself prior to O365, I found it frustrating to have to guess at the issue for several hours before someone finally posted an outage notice that confirmed my suspicions. But...they did have it resolved later that same day and it has not happened again since.
6. We are not a government entity and we did not limit mobile/byod options...anything goes around here, we support it all. Sorry - can't help with this one.
7. Nope. And we have minimal bandwidth to begin with so it was a concern....but in our case (again, small company <150 people) we didn't see any impact.
8. We did migrate Sharepoint to O365...but we were coming from a hosted Sharepoint Foundations site that was used very little. We had a workflow and some document repositories that were a little tricky to move but with the help of Share-gate (http://en.share-gate.com/), it wasn't bad at all.
9. This is a tricky one....iPad users seem quite happy with it...iPhone users not so much. Android users have all but given up on anything other than email & Lync. Windows phone/tablets seem content (go figure) but I only know of 2 users with Windows mobile devices. One big issue is the certificate needed for authentication. iOS devices are easy enough to setup with the use of the iPhone Configuration Utility...once the cert is present, they work just fine. Android on the other hand does not like the use of self-signed certs for this purpose. I'm still working on a reliable solution...and that's just for phones...as there is NO O365 for Android tablets at this time. When you look at the Phone & Tablet software offerings in the O365 portal, your choices are:
Phones: Windows, iPhone, Android Phone, BlackBerry, Nokia (Symbian OS) and Other
Tablet: Windows 8 tablet, Windows RT device and iPad
That't it! So...if Android tablets are popular in your environment, this is a major consideration. Another item to point out...not every app is the same between devices. On an iPad, you can download Word, Excel, Powerpoint, OneNote, Outlook Web App, Lync, Sharepoint, OneDrive for Business...each individually. On an Android phone (not tablet), your only choices are OneNote, Lync and "Office"...the Office app combines Word, Excel and Powerpoint under one app but so far, seems much more limited in functionality than its iPad counterparts. iPhone gets a hybrid of the two...iPhones can have Sharepoint, OneDrive for Business, Lync, Outlook Web App and OneNote individually but then Word, Excel and Powerpoint are lumped together in the limited "Office" app like on Android.
And just to be thorough....the software available to phones running BlackBerry, Nokia or Other is basically nil...they are listed because it is possible to configure them with email through O365.
10. We went all in with the Microsoft cloud offerings...we use MS Intune in conjunction with O365. No third party products at this time.
11. MS Support has actually been decent. They are responsive when you call in. They seem to be able to resolve most issues in a timely manner. My biggest complaint about support so far has been that one day when it took them nearly 4 hours to acknowledge the relay issue. But that was post-migration.
12. More user training early on!!! The leap to Office 2013 warranted training alone...but going to the cloud, with huge dependence on OneDrive for Business in place of local storage and Sharepoint integrations galore has been confusing for our users. But, I think that depends a lot on what your users are currently used to to begin with. I spend way too much of my time training users how to use Lync...but they are new to Lync with the O365 leap so that is to be expected. Had they had Lync before, I don't think they would've even noticed. And the mobile devices....since O365 allows you to install on multiple devices, people are doing so....and that means more questions and more training.
13. This is another one my particular case doesn't really translate well. I will leave it up to others to draw the comparison you are looking for because I don't have the appropriate situation to pull from.