Hi Glen,
Depending on what you are doing you shouldn't have too much trouble switching to Numbers, which is a powerful and pleasant environment for personal and some business projects (but not so good for large datasets). Numbers can open (and convert) most Excel documents, and the functions it has in common with Excel work the same way. Numbers doesn't, however, support most "array" functions, so (fairly simple) workarounds are needed that people in this discussion are good at providing. Also Bear in mind that Numbers treats dates and time differently from Excel, introducing a "duration" data format and related functions that Excel does not have.
Numbers has a table-centric design. Unlike Excel, where typically have large expanses of cells in a sheet separated by blank areas, in Numbers it's easy to break your work up into multiple small tables on the same sheet. You'll probably want to modify the format of some of your Excel documents to take advantage of the Numbers design. See the built-in templates at File > New in your menu for good examples of how to organize projects in Numbers.
SG