I think the first thing to bear in mind is that the Spreadsheet application in MS Works is extremely basic compared to Lotus 123. The equivalent Microsoft program is Excel.
<<<What is the purpose of the large outlined cross when you open a Spreadsheet, and how do you get rid of it?>>>
That is the default "mouse pointer" used to click on cells, highlight them, drag them and so on. The same "cross" is used in both Works and Excel.
<<<What does the warning "your footer is too tall" mean. Can't find it in the Help files, and it doesn't seem to make any sense.>>>
I would suspect that you have imported an incompatible page setup from the original Lotus file into the Works spreadsheet. Have a look at the Page Setup settings.
<<< Printing. It insists upon including the Row number in the printout, whereas Lotus did not. I can't see any point in them being included in the printout - how can I get rid of them?>>>
In the "File > Page Setup" menu, select the Other Options tab and untick PRINT ROW AND COLUMN HEADERS
<<<Why does the printout not centre the Spreadsheet? At the moment, those that are too big for Portrait, but do not fill Landscape, are aligned to the left-hand side. This should be automatic.>>>
The feature isn't available in Works. Even in Excel, the option to centre vertically and horizontally has to be specifically set within the page setup - not everyone wants a spreadsheet centred vertically so that it is half way down the page, although it may be desirable to centre horizontally.
<<<It is disappointing that, when altering Cell Width manually, it does not display the numeric width as Lotus does. One is left to visually judge the distance.>>>
The column width isn't shown when dragging it to a different size, as it is in Excel, but its size can be selected in the menus - "Format > Column Width".
If you need the sophistication of Lotus 123 then you would be better with Excel. You may also have noticed that Works only has a single "sheet", it doesn't support multiple sheets in a "workbook" like Excel.