Hello Hirantha
It looks like you did a excellent job selecting your hardware. If you order the net4801-50 board and lan1621 card directly from Soekris they will make sure that the right case is included. For power supplies, Soekris model # 31211225 (2.5 amps 90V-264V) is suitable for non-US power. It's only $2.00 more than Soekris model #31211215, which is rated for 1.5 amps.
My company is currently has two Soekris net4801-50 routers in use. Both of ours have the 4 port lan1641 boards installed, and one of them has the vpn1411 hardware crypto card onboard as well.
If the possibility exists that you may expand your network in the future you might want to consider paying the extra $32 for the 4 port lan1641 card versus the 2 port lan1621. Having the two extra physical interfaces has proven to be very helpful to us. Our primary Soekris currently has 85+ client PCs attached to it, 9 network printers, 12 servers, a PBX, a wireless router, and a VoIP gateway device-all across six LAN subnets.
Hope this helps.
Chris
Edited to add: Our secondary Soekris uses a SanDisk Comfact Flash card and it works perfectly.