Edited for spelling We have not had the opportunity to make the code for the uploading counter depending on membership level. Therefore the daily limit for the number of pictures uploaded is set to 9. But please, don't upload 9 images in a post! Members without a fast connection will not have a nice experience.
The 900 pixels size on the widest or tallest side is the guideline, so people with regular sized screens at regular resolutions don't need to scroll left and right or up and down to see an image. It is up to you.
The Galleries allow for much larger images, up to 1800x1800 pixels and 10Mb weight. Again, we recommend you keep them at 1204 or 1280 pixels at their longest side; once more for the sake of those not a fast Internet connections. But it is up to you.
The Other Camera systems and formats forum was in fact created to allows for discussions and of course images made with any camera brand and/or lens, whether Canon, Minolta, Exakta, Hasselblad, Sony, Sigma, etc.
Your images made with a Nikon camera and a Nikkor or a 3rd party lens are welcomed everywhere on the community.