> Is Tikiwiki strong enough for hundreds of users?
Yes, there are many sites with over 100+ registered users online at a single time. One which Im hosting has 12000 registered users and regularly has well over 100 online.
And if I use intensively file galeries, is it ok to have hundred of files (ok, maybe 1000 files) in galeries ?
Set the file galleries to store in the file system rather than the database, the same for image galleries and you wont have problems.