Is AD Certificate Services necessary to migrate

Are you planning on having a SINGLE Server 2016 that is both your Domain Controller and Exchange Server?  Since SBS is no longer an option, you need to know that installing an Exchange Server on a DC is highly NOT recommended.

And please don't take this the wrong way -- but your question is actually a demonstration that you truly don't have the training or skills to properly manage the complexity of putting an Exchange Server 2016 on your DC.  

That being said, your only option is to install Server 2016 as a Hyper-V Host and then install two virtual servers (one as the DC and the other as Exchange).  You should be aware that the estimated hardware, licensing, along with backup hardware and licensing costs will be about $20,000.00 for 50 users.   (it could be higher if you have to upgrade workstations and Office versions to be compatible with 2016)

There are much more efficient, economical and reliable solutions -- such as integrating Office 365 -- and I hope you have considered those.

I know this is not the answer you came here looking for but I felt that it is important to point out.

As for migrating your CA?  Read that exceedingly long article and see how it applies to YOUR specific environment -- because only then will you know if it is applicable.

Are you planning on having a SINGLE Server 2016 that is both your Domain Controller and Exchange Server?  Since SBS is no longer an option, you need to know that installing an Exchange Server on a DC is highly NOT recommended.

No, Exchange will run on its own VM.  I will have two different DCs, within VMs, each on a different physical host.  Plus 2 more VMs for file sharing and Timberline accounting software.

And please don't take this the wrong way -- but your question is actually a demonstration that you truly don't have the training or skills to properly manage the complexity of putting an Exchange Server 2016 on your DC.

That's why I'm here.  I actually was MS trained in Server 2000 way back when...but have not really dealt much with much of the AD minutiae, as I only service a couple SBS installations.

You should be aware that the estimated hardware, licensing, along with backup hardware and licensing costs will be about $20,000.00 for 50 users

Not a bad guess.  We're at about $19,000 including 60 CALs for Windows and Exchange, licensed for up to 6 instances of Server 2016 Std VMs, and the dozen necessary Office upgrades.  I'll probably continue to use the backup system we have in place.

There are much more efficient, economical and reliable solutions -- such as integrating Office 365 -- and I hope you have considered those.

Economical?  Not by a long shot.  Not when you estimate a 7+ year life span of your software and hardware (and my Server is 9 years old and still works fine).  Office 365 is $12.50/mo/user.  That's $9,000 per year times 7 years is $63,000.  Of course, that's assuming I do all the maintenance, which I do.  Even at 3 years, the average version span of Exchange, it's notably more expensive, which if you considered the labor for maintenance, probably does no better than breaking even.

Reliable?  You're probably right, but it depends on your point of view.  Any problem that comes up I can fix.  If Microsoft has an issue, I'm at their mercy.

Efficient?  Yes, it saves me a couple weeks of time (every 9 years).  But keep in mind, we get a much better product - 100% SSD local on-site Exchange with dedicated hardware.

So, yes, we considered them, and weighed the benefit of having the latest software every year, but did not feel that those benefits outweighted the costs.  Of course, that's just my opinion, and it's not for everyone.

As for migrating your CA?  Read that exceedingly long article and see how it applies to YOUR specific environment -- because only then will you know if it is applicable.

Well, I did read it.  It tells you how to migrate the CA.  I'm sure if I follow each step, it will eventually be migrated.  It doesn't say what it does or what's going to crash if I screw up.

I just re-read your comment that you only upgraded about a dozen Office licenses... even so, I think my productivity example saves money over the term.  :-)

Again, personal opinion: $500 for Office volume licensing is a rip-off.  Office Home & Business digital download is $188 on Amazon.  I know, I know, people can tell me about how much better it is, being able to install via group policy, extra programs, and whatnot.  But seriously, I think businesses should get a discount for buying in bulk, not be charged a premium.

Perhaps there are time-saving features in the newer versions of Office.  I know it sounds good on paper, but the way I see it, Word works about the same as the 2007 edition.  Outlook 2010 added the ribbon toolbar, and in Excel 2013 they finally made Excel opens files in separate windows.  (I've not used 2016, since it doesn't work with Exchange 2007.)  And keep in mind, if you're going to upgrade people all the time, you have to subtract all the time that users spend trying to learn a new interface - which is considerable and can easily outweigh benefits.

Thanks for your comments and help!

Just FYI, since updates happen every couple of months, there most likely won't ever be another major interface overhaul... Microsoft recognized that to be a problem, and is a major consideration of how the Office 365 Pro Plus updates are designed.  This is also true of releasing features regularly -- people can digest a list of 5 or 6 new features and determine if any are applicable to their work.

My point is that there is absolutely a difference --- not only in features, but in the methodology of how people work.

Best of luck with your migration!  :-)