sbs 2003 replacement sbs2011 or 2012r2, exchange 2013, RDS

We are a small a small accounting firm, 35 users, and have SBS 2003 r2 using exchange 2003.

Our LOB apps are Quickbooks and LaCerte and Microsoft office 2010, our desktop/laptops are i5/i7 Windows 7.

We cannot and will never use anything in cloud, except backup.

We have remote site in near future that will need access to an RDS for 5 users max.

Our present server is Dell PowerEdge SC 1430, dual Xenon x5110 1.6 ghz, 8 gig ram-4 useable, 250gig raid 1.

Our exchange database is under 40 gig since starting it in 2007, our data stored is at 100 gig for same time frame. We also use RWW now, but will have need for the RDS. We will not go over 50 users in next 5 years.

Everything works great. They want exchange and like the calendar sharing.

Senario1: I am looking at SBS 2011Std, I know it is getting old, but it would cover our exchange needs and Domain Controller and RWA, file server, then add 2012 r2/RDS for the remote site. Two separate servers.
5 years with SBS 2011 is acceptable.

Scenario2: Use 2012r2 as domain controller on POSE, Exchange 2013 on POSE and RDS on POSE, Quickbooks and LaCerte do not recommend using VOSE on a RDS. Microsoft does not recommend Exchange in VOSE on a POSE running domain controller on POSE. This is mission critical and we cannot experiment to make it work, if MS does not recommend it, we will not use it. This setup involve 3 separate servers. 3 W2012r2, plus all the cals for Xch, RDS, and server.

Again. Microsoft does not recommend Exchange running on DC, nor RDS running with Exchange, nor do they recommend virtualizing a DC for mission critical setting, QB and LaCerte cannot be virtualized. No cloud anything.

If you have a better setup or hardware recommendations for the above two scenarios, please respond.

Thanks