I would say several websites, especially any sort of gaming fansite, has a header logo above 100KB. One of my websites has a header logo of about 180 KB and a footer image of 123kb. Hell even the page bg is 105KB.
Why? Because the website is visually appealing and intricate. Now I am not suggesting that you raise the file size to astronomical proportions, but 100kb would be low for several websites that have any sort of graphical appeal.
And if I may be so bold as to comment offering 1TB space and transfer is ridiculous, even though no one will remotely approach that. You are more likely to draw negative opinions for this offer, then if you offered say 1GB space and 10GB transfer, still difficult to achieve with that size restriction. You may comment that the offer for space and transfer is to entice people to join, but how many will really want to join when they see a 100KB limit for files when they can goto any competitor and get much higher?