Without good promotion on other game forums (MMORPG based and prv. servers) will get ~50-100 max. online players.
NON FAIL (yet) L2 servers where they still have some players on:
1. http://www.l2world.org/
2. http://server.lineage2media.com/
3. http://www.l2gang.com/
DDoS'ed by some skiddies, hmm.. i don't think so maybe only DoS, only if your server is on Win. XP or 7 (with direct connection without a router or external firewall, if you don't know how to configure iptables).
Possible DoS if you are on:
- Windows 7 or Windows 2k8R2 and you don't have IPSEC =ON/Ok.
- Linux if you don't have good configuration for your IPTables firewall.
- If your DNS's are NOT protected.
etc.
Anyway Good luck!
Maybe this info will be good for you ;)