Our custom feed is currently incompatible with Web Platform Installer 4.0 RC and Beta releases. There is a bug in the WebPI 4.0 which first needs to be resolved by Microsoft. Issue has been reported to Microsoft by multiple parties.
I highly recommend using the manual installation method as it contains the latest version of MonoX. You can download MonoX package on this page
. There is also a tutorial which shows you how you can install manually here.
The errors which you were receiving are pointing out that your password for the 'sa' account is wrong. Can you please verify the password?
Please also make sure that SQL Authentication Mode is enabled on your SQL Server. This MSDN article
explains how you can enable your 'sa' account and how you can enable SQL Authentication Mode.