1. The no. of controls does affect the page performance per se. Controls that are server-aware are notably slower to render than pure HTML controls. I think the page performance is more dependent on the server side processing being done (such as the code you write on Page_Load.
2. 3000-3500 items in a dropdownlist ! That's quite a lot, don't you think ? It would be much better to retrieve data on-demand (such as in an Ajax- based Autocomplete textbox). So many items would definitely slow down the page. Also, the selection of a single item in the DDL should not freeze the page, unless you are running a javascript that does some looping on the items themselves. 3. Depends on what you are doing on the postback. 4. In a live multi-user system, your current implementation will surely result a very poor user experience and heavy server load. 5. Tab flows can be minutely managed by setting tab order explicitly.
