I agree with the others here; not sure how the 649GB was calculated (please share), but...
Assuming basic requirements of 12 hours of continuous recording, 10fps, average frame size of 34KB (This might be a little high, but just an assumption) assuming H.264 VBR, 1080P resolution, at 260 days for 300 cameras, that puts the storage at more like 1.1 Petabyte and required bandwidth at ~800Mbps aggregate at HQ for just the remote sites. You still need to consider the storage for HQ cameras, so a total of ~1.9 Petabyte of storage will be required assuming the listed assumed requirements; bandwidth on the local network to the SAN will be on the upwards of about ~1.4Gbps, assuming average bandwidth per camera is 2.7Mbps (This will vary on scene).
You will NOT be able to use Etherchannel; Etherchannel does not move over any traffic load when link saturation occurs. Traffic through a specific link is based upon a hash on the mode being used. You will more than likely have to utilize a direct FC interface card on the Milestone and connect to the FC port on the SAN.
At this point, I do not believe that an E2700 Netapp device will be adequate for the solution based on the assumptions (much of that was not provided). You are definitely going to need expansion shelves to whatever device/vendor you go with due to the amount of storage required.
Something else to consider:
Internet bandwidth costs: ~$50,000/Yr
HQ - ~1000Mbps: $3K/mo (+/- a few hundred dollars); depending on vendor and location, there might be an affordable solution, but here in Hawaii, business bandwidth is expensive.
Business Fiber Internet 50/50 ~$100.00 (20 sites, 2K/Mo)
~50K a year just in bandwidth charges
Storage costs: ~$250,000 (Includes support/warranty costs for 3 years)
Initial Cost of a 1 Petabyte storage solution can cost you nearly $250K - $2.8 Million dependent on the vendor and hardware you choose for the storage solution. The raw drives alone can cost you roughly $43,000 per Petabyte; if you shop around, you can maybe get to ~$38,000. I definitely would not stripe that to a Raid0, so with Raid5, you are looking at ~$114,000 - ~$139,000. If considering Raid6 or 10, that will increase the cost of the drives and hardware.
You will definitely need to contact Pre-sales support at Milestone to ensure that you have adequate server resources to support the solution as already mentioned.