In terms of question 1, the following KB article should be able to give some guidance:
For question number two, the data will need to be manually refreshed periodically if using Tableau Desktop, and if it referencing a new file, then the connection will need to be edited to point Tableau to that file.
Are the "24 Excel" 24 worksheets in 1 file or 24 different files?
In the first case, one idea that is not in the (otherwise excellent) first KB article is that you could use Custom SQL to do a UNION of the 24 worksheets, since they all have the same format. Then you end up with one data source in Tableau and building your 1 report gets a lot easier.
In the second case (24 files), it's possible to get to the first case by having one Excel workbook that has ODBC data connections to all the other workbooks, so it effectively has 24 sheets and then those sheets could get pulled together in a Custom SQL query.
How would I go about suggesting that the KB article http://kb.tableausoftware.com/articles/knowledgebase/join-vs-relationship-60 have a section added on using Custom SQL to UNION data? I think it's a common-enough question on the forums, for example when someone has worksheets for Jan/Feb/Mar/etc. and left/right/inner joins won't work.
If these Excel sheets don't change, I would use the RDBmerge add in to bring them onto one sheet. No good if the data changes though