What does the main page (index.php / stb.html) display by default ?
Can it be changed to display a maximum of the last 7 calendar days postings and can a 'start of week' day be set? In other words, if i want my week to begin on a monday and today is eg, Wednesday, can i set the blog to only show Mon, Tue and Wed's posts ?
What the main page displays by default is set in the backoffice, on the "Settings" tab. You can set the display mode to "days" and then set the number of days you want it to show (7).
The setting to change the first day of the week is at the bottom of conf/_locales.php.
By default, b2evolution will not show any posts in the future.
I don't think there's a way, though, to set it to show "only this week, up to today". At least, not without some hacking.