Surely you must have a local vendor in your city that you can get this equipment from? I'm sure most vendors would gladly assist you since you need to get the more expensive stuff.

I would think you need the best you can get, I'm not sure here if we are talking about 300 concurrent users, because that is 60MB/s and you would need dual gigabit nics and gigabit switches throughout the main part of your network.

Talking about hardware, you would go for the best. The best motherboard, maybe xeon quadcore processors but those are really pricy when going for 2,5-3ghz. 8 Gigs of RAM. For storage, you would need a SAN for those amounts, but it would be nearly impossible to get anything else than SATA, expecially if you want to do use Raid 1, you will need 6 x 2TB drives. You should consider getting a good HP Proliant or Dell Poweredge.

Good luck to you