What are the maximum volume sizes and maximum file sizes for the various Windows file systems?

actually, you can format FAT32 to more than 32GB, but internal limitations of SCANDISK limit you to 32GB. So you're not safe on ME/98 boxes. see http://www.dewassoc.com/kbase/hard_drives/hard_drive_size_barriers.htm for HD/OS size barriers in depth. the individual drives are limited to 2.2TB due to 32-bit addressing limitations, but the volume size apparently can be larger. Now that we have 1TB drives, this limit will soon be a problem and we will need new OSs or an OS patch & new filesystems to run the bigger disks.

Has anyone read about additional ntfs volumes

I recall reading somewhere that the 256TB size is applicable when combining volumes, like with spanned, mirrored or striped volumes

I dual boot ME and XP.
For compatibility, when I initially installed XP from ME I formated a SATA 160Gb drive from the ME command line to a single 150Gb FAT32 partition and then installed XP on this partition.
Works fine, very few disk related problems.

does anybody know what will change in WinFS?

For the question on mounting points, it's possible to mount a unmounted or mounted volume in an empty NTFS directory with graphical tools.
You can use command line tools as described in http://support.microsoft.com/kb/205524/en-us#kb1 .