50pplus doesn't require that yo save an image anywhere and store it, you just need to "Copy Image Location" (right-click) from your browser and then paste it within the "IMG" tag in your posts.
I generally save iamges to my computer for backup...but I also like http://www.photobucket.com - and even pay a whopping 99-cents per month for ad-free access (if only 50plus premium was so cheap, LOL)!
Not sure what you mean by "properties of the gif"....but if you mean size/dimensions, etc you would have to open it in an image editor. I use Photosho CS but there are free ones as well, such as GIMP (http://www.gimp.org)
I occasionally have problems getting images into posts and find that I then need to upload them to tinypics first and copy from there. When you upload to tinypics there is an option to resize your image. I usually use the web size.