Number of tablespaces doesnt matter, we have a datamart with around 200 tablespaces right now and expecting to grow to 800 or so in one year time (uses read-only tablespaces, one partition per tablespace)

Your database sounds like DWH (RAID 5), if it is then you dont need to run the db in archive log

Size is up to your own choice but IMHO a 100GB database can perfectly have 2GB datafiles or 4GB inclusive depends your OS limitations

One controller doesnt seem enough, may be it will be your bottle neck in the future (even your controleller is fiber optic one is little)