Read some ponderings: http://forums.adobe.com/thread/991455?tstart=0
an Intel SSD on the server,, will it do the job???
Umm, no. You're not running a database server, you are running a file server. SSDs are only fast with small amounts of data, not huge media files. You will need a proper RAID 5 system. The network setup should not be a problem, but as in the thread I pointed you to, the key point is to isolate the render farm from your everyday stuff to avoid resource conflicts...
15K or 10K or 7200 HDD in RAID 5???
can u also tell from which will i benefit more: more average speed computers vs few fast computers???
The drive speed of the individual disks in a RAID is secondary. I/O throughput is determined by the number of disks, the host interface and the number of controller channels that can be combined to form the RAID. Invest money in a proper hardware RAID SATA 6G controller/ motherboard, then plug-in whatever disks you can afford - ideally all of the same size and make. The rest of your question is not easy to answer and will ultimately only end up in the same dancing around like questions regarding multiprocessing - for one kind of project one setup may work best, for otehrs another. This will depend a lot on wheter you only render simple stuff that even weaker machines can render reasonably fast or heavy comps that only your most powerful machines can handle whiel the lesser ones will be skipped or take so long that they barely contribute....