It's a DoS protection, not DDoS. You don't have to disturb it, 1024 is a perfect value, not too few, not too much, and it's enabled by default. Note that it's protection is limited, there isn't much one could do against 1 GBit DoS, but it's quite useful everything up to ~100MBit (ofc only if your net is faster than the attacker's).

Since there are no proper CE->PC map converter, I don't think playing CE maps on HPC will be ever possible. Also, I don't see the point anyways why anyone plays Halo PC when there is CE.