Really it depends on how much you actually know about the data and what you're planning to do with the data downstream.  At the end of the day 20,000 columns...

Why are you doing this in SSIS at all, this can be done in one line in powershell as simply as

Move-Item "C:\Test\input.txt" ("C:\Test\input" + (Get-Date -UFormat %b-%Y) +...

Well are you adding more data to the DB every month?  If so reindexing will take longer 😛

Well if he wants permissions more granular than AD groups then he has to use logins more granular than AD groups.

Don't know if this has been discussed elsewhere but are backups and restores also possible between linux and windows?

Well technically you can also just use sequential first/last names 😛  

Firstname1, Lastname1
Firstname2, Lastname2
Firstname3, Lastname3
.
.
.

What are the exact errors do you get from CHECKDB?