[Updated 3/25/2017]
During the installation of Skype for Business 2017 you may run into errors if you select ‘Connect to the internet to check for updates’ and you also change the default installation location to something other than the C:\ drive. There is a potential third variable that might be required to run into problems as well: If you do not initially deploy conferencing during the front end pool wizard in topology builder. (Additional testing would need to be done to further isolate it from here).
The error that you may run into actually happens later, during the server component installation, and it is:
failure code 1603
Error returned while installing OcsMcu.msi, code 1603. Error Message: A fatal error occurred during installation”
The solution was to uninstall just the Skype components from control panel and then re-run setup. Only took 10 minutes so wasn’t too big of a deal. But now we must remember to manually apply the latest cumulative updates after the installation completes =)
The Uninstall order (for what it is worth) is the following:
(First uninstall XMPP then proceed with uninstalling the core components last). It is not necessary to remove all the language packs and local SQL instances (at least in my case it wasn’t).
At this point you will be able to successfully complete the full installation of Skype for Business. But you are not out of the woods yet! Because when you attempt to apply the latest cumulative update (in my case it was February 2017) then you will have that same Error 1603 on the Conferencing Service (OCSMCU.msi). When digging into the log files it appears that it is trying to find some files on the C:\ drive despite that during the installation, we selected a custom install path to the E:\ drive. 
The solution for me was to uninstall again a 2nd time, and this time I updated the Topology builder to include all of the AV Conferencing Options.
So my recommendation is to deploy to the C:\ Drive (just make it a large drive like 250GB) and to initially deploy all of the conferencing features to avoid these issues.
The Cloud Technologist 