rezag - 250 is a lot. Do you have KeepAlive enabled in Apache config? If not, try to enable and see what will happen with connections.
Yogesh - I would personally start with something like 100 connections and block time for 1 minute (60 seconds) with email notifications enabled - this way you'll get an email when some IP will be blocked and will be able to see if this will affect your actual site members. Even if it will quick block for 1 minute shouldn't cause much harm. Once you'll settle to specific number of connections it will make sense to bump block time to 600 seconds (default) or higher value depending on how often you'll be hit from the same IPs.
It is extremely easy to install (D)DoS-Deflate - all that needs to be done is to copy & paste commands listed in the installation section at http://deflate.medialayer.com/
Once tool is installed you can edit its config located at /usr/local/ddos/ddos.conf to adjust blocking type (APF / iptables), number of connections, block time and email address for notifications. Any text editor like "vi" can be used to edit the file. Alternatively you can access the config file through tools like WinSCP.