1. Not sure, for 1.4.5 sth around 30MB. 900MB MorphOS partiton here.
2. You mean a partition with boot.img probably. Boot from FFS partitions is supported by all SmartFirmare versions (latests can boot from SFS too). For all other partitions use SFS it's better IMHO :).
3. Sure, why not? MBR partitioned drive would be an evil ;).