Also, how do you fix a "slow database" when you don't know exactly what is slow? Do you have benchmarks? A list of the most used stored procedures?

Of course, if you want to recover the records you deleted, and you're in Simple Recovery, you're out of luck. You'd have to restore an old copy of the database...

???

Recovery models don't have anything to do with what SQL works in a database. That's controlled by the Compatibility Level the database is set to.

A data warehouse is just another database with a star schema instead of a standard 3NF schema.

You're looking for something called Market Basket Analysis. 
This article might be helpful

We can't see your data. How are we supposed to advise you?
PowerBI is sort of cool, but the fact that you can't write back to sources BLOWS.

use SSIS instead?

DECLARE @start_date date
DECLARE @end_date date
SET @start_date = DATEADD(YEAR, -1, GETDATE())
SET @end_date = GETDATE()

Instead of the above value for @start_date, you could do something...

Should be in the ExecutionLog
https://docs.microsoft.com/en-us/sql/reporting-services/report-server/reporting-services-log-files-and-sources?view=sql-server-2017

Here's a really helpful article I found...
https://www.sqlchick.com/entries/2011/2/6/querying-the-report-server-execution-log.html

Sue's right... I think your question is backwards... SSRS reports connect to databases...

Difference between what? The SSI1, SSI2, and SSI3 columns?
If they're dates, use DATEDIFF(), otherwise just subtract.

That's how input parameters are declared. That's just how T-SQL works.

Why are you VARCHAR columns and then storing numbers in them? Why is a column like Withdraw_Percentage not a decimal or similar?

I would like to create a stored procedure based on anexisting table, where the stored procedure will automatically create a newtable with additional columns of data in the right...

How far did you get writing this? Pretty good bet that nobody is going to write this for you.
And what's the deal with all the NVARCHAR(MAX) columns? What are...

Putting all the files together on one drive invites a single point of failure disaster, so that's just plain wrong. Say they're all on the same drive, and the drive...

Can you go back to the person that created the dataset and ask them to add it? (super annoying, but I have no idea how else to do it!)