I used to work at a company that did healthcare data reporting.  I was stupefied when I found full names, birthdates and SSNs in the database. Went straight to the...

Remove the defaults. You need at least one that doesn't have a default value for SSRS to prompt you for values. Otherwise, the report will just run with the defaults....

You do realize that the data types for your parameters and the field types and sizes in the underlying table don't match, right?  If you want to pass multiple values...

Sounds like you need to put a rectangle on your report and then you can put the textboxes inside of it. That way, you can arrange them like you can...

Why not play with each one and decide for yourself? R support is already built into SQL Server.

I got the chunks apart... So I guess it's a place to start.  You need Jeff's string splitter function for this, which is here.  And here's my code......

Got Google?
http://sqljason.com/2010/12/subscripts-and-superscripts-in-ssrs.html

Got it to work... probably a kludge, but ...Summarized in T-SQL first:
SELECT SalesRep
    , SUM(Sales2016) AS Total2016
    , SUM(Sales2017) AS Total2017
    , SUM(Sales2017) - SUM(Sales2016) AS Delta

That's a drilldown report. It's covered in Brian Larson's book... and probably all over the place.  Here's a super quick video on YouTube.

Okay, just tried it with my own dataset.  Turns out, I can't find a way to sort on an aggregated column in a matrix. 

So if you base your...

Don't think you need a new dataset. What you're describing sounds like you need a Matrix on your report.
Group on [Diagnosis Code], then at the intersection, do COUNT().
You...

Got Google?

http://sqlmag.com/t-sql/group-all

Did you look up the differences between DECIMAL, MONEY, and SMALLMONEY?