How to size centralized storage solution

Hi...

Since I am new to storage, I would request your kind help in determining points to be taken care while sizing centralised storage solution for eg..clarion.

My contention area is :

1.How much Bandwidth is required from servers to storage: how do i calculate this? This will help me in identifying whether I need to go with iSCSI or FC and justifying the same.

2. What combination of disks, I should have in my storage appliance i terms of High speed FC, SAS or SATA or SSD.

Assuming that I have 5 applications/services...ms exchange, SAP, AD, DNS, DHCP and would eventually virtualize these applications on vmware using two small servers. No. of users can be taken as around 150.

I need to justify the criteria of designing strorage solution in terms of what bandwidth will be required between servers and stirage devices as well as selection of disks inside the proposed central storage device.

Request you to help me in understanding the criteria behind selecting appropiate clarion solution in terms of points mentioned above.

(Note: I do have prouduct idea about clarion)

WIth Best Regards & thanks in advance