Wi-Fi network for 200 users accessing local web server

I'm planning a network for charity and fund-raising events at which typically 200 users will need wireless access (via tablets and smartphones) to an auction website, hosted locally on a server at the event location. Each event will typically be in one large room or hall, so there should be no issues with wireless signal coverage.

I envisage I will need a web sever, able to handle say 50 simultaneous accesses to the local web site at any one time, a wireless hub (DHCP server), a network switch and a number of WAPs.

Also, it would be great if on connection to the wi-fi network the user is taken automatically to the local auction website. Is this possible? If so how?

I'm after advice on how best to implement such a network. The issues I've thought of so far are as follows:

How many WAPs would I need?
How should they be configured/connected (wireless or cable)?
How is DHCP handled for 200 users?
What would the specification of the web server need to include (to handle say 50 simultaneous accesses)?
What about SSID and security?

Is there anything else I need to consider? (I'm sure there is :-)

Finally any recommendations on hardware?

Thanks