You do not neccessarily have to have Gateway and Remote Apps, but it is recommended. Since your users will connect via a VPN and not through the web it is not neccesarily needed. Locl Disks are still needed as all users will still have a profile on the TS box. To figure the exact amount you need, find the size of your default profile, multiply that size by 100 then multiply by 2. Then add the required space for Windows and all programs again multiplied by 2 and add to the user space total. This will give you a good rough estimate of the space required for each TS box.
1.If my application e.g. take 100MB of RAM when I need to RAM as 100MB X number of current users ? Concurrent users yes + add 3GB for Windows and background services.
2. For the networking card, , if the user access and the web servies for app access are on the same LAN, how can I take advantage of 2 NIC? The network cards can be bridged effectively with network load balancing, doubling available inbound/outbound bandwidth.