A few thoughts..
Migrating a VSS repository to SVN can be a nightmare, specially if your VSS repository contains shared files between projects or if any permanent deletes has been performed.
Do you use labels in VSS? In SVN, branches must be used to replicate the VSS's labels. Even if you don't see usage in branches now, it would be a good idea to plan the structure with them in mind.
SVN doesn't have exclusive checkouts like VSS. However, the same idea can be achieved with locks. Property svn:needs-lock can be useful in this context.