Questions 1 and 2. I'm sure that they do at least by a small amount, but given that hard drives now come in hundreds of gibabytes in capacity, does it really matter?
I prefer stored calculations in most cases as they produce shorter response times when performing sorts, finds and when pulling up report layouts that access very large numbers of records. There is a performance hit from this approach when you need to import data into such a table--say from a back up copy or when deploying an updated file--but since such imports are much less common than searches, sorts, etc. I find that the more reasonable trade off.
With regards to your report, can you post a "mock up" of what it needs to look like? Your basic choices are to either use summary fields in a summary report, Summary fields in filtered portals, or calculation fields with the Sum function and the appropriate relationship to match only to the records that need to be summed. In each case, you add more fields and perhaps more table occurrences to your file.
Also what fields do you have in your table to identify the: Week, date, and/or year?
here is an image of the report I am trying to recreate I have done that in Visual fospro which was very easy because there was a function to summarize all fields of a range of records into an arrays then parse the array into another temp table
You appear to have multiple tables involved here and different YTD and previous YTD values you need to pull from each.
I'm inclined to use a "self join" with a summary field for each YTD and PREV field.
Here's a simplified outline of the method, using just one set of YTD and PREV values:
Define two fields in Cash Reciepts: sTotalCash, cYear, cPrevYear
Define sTotalCash as a summary field computing the "Total of" your CashReceipts field.
cYear is defined as Year(DateField)
cPrevYear is defined as Year ( DateField ) - 1
Make two new occurrences of CashRecipts and link them like this:
CashReceipts::cYear = CashReceiptsYTD::cYear
CashReceipts::cPrevYear = CashReceiptsPrevYear::cYear
On your layout, add CashReceiptsYTD::sTotalCash and CashReceiptsPrevYear::sTotalCash to your layout.