I need some help.

I am trying to design the most cost effective but stable and secure network/server setup for an ecommerce app we are building and would like your suggestions opinions on it in terms of a network setup and hardware as well.
We are shooting for approximately 100.000 page views/day in 4-5 month resulting in 5.000 daily transactions. not much budget at this point something like 13k for the whole thing.

here is a diagram that i am playing around with:

http://www.geocities.com/arainx/


Questions:

If the isp doesnt provide a router/ is linux router a stable/secure option?
Does anyone have experience with this product: http://www.imagestream-is.com/R1_Features.html, what other low cost options do i have besides for cisco?

If i go the route of building a linux firewall machine what considerations should i make or leasing watchguard firebox. Can the firewalling be done at the linux router?

What kind of switch would I need or a hub would do? Could what I am trying to do be accomplished with 1 linux virtual server (cluster the webservers together and database for high availability? Is anyone using coyotepoint e250 or is it too much for this kind of traffic what about cisco local director? I am planning on leasing those for 12 month.

I am thinking about the following for the mysql db setup:
master mysql on it's own box. 2 switch-controlled-load-balanced app servers on
their own boxes. each app server runs localhost mysqld as slaves to the
tcp/ip master. all writes to db go via network to master. all non-critical
reads (meaning they can be off a little bit) go to localhost slave which
will get the data pushed to it fairly soon. all critical reads will be made
directly from master. A question I have is How is the ip takover done if the master dies? I would want one of the backup slaves to become the master.

What other methods could I use to make the access secure to this setup at the colo? ssh? And what terminal server would I need? what am i missing from this setup?

I really appreciate your input.