It would be nice to have an ajax section, on post/pm edit, that allows you to upload pictures to the server and it gives back the proper [.img]linkhere[./img] stuf to be added between post/pm text.
Why ajax? to upload several files when writting a post/pm... one by one, without leaving the edit page.

+ some options (closed, only admin touching it... or maybe leaving it open to members, as an option taken by admin), like image resize (for maximum proportions, to decrease/optimize file sizes)

+ this nice idea http://www.smfpacks.com/b147/off-site-photos-copied-forum-server/2451/ as a plus, an option to be run by the admin (by hand mostly, not automatized)... it would be nice if the images "imported" are resized too (previous point)... it should use dates as mark point, so do not parse "old" posts? already parsed before

+ maybe a way delete images uploaded by mistake (but, how to avoid angry members be able to delete all their image uploads? maybe just allowing image erase when editing... or using a time period/range)

http://www.smfpacks.com/au with this https://github.com/Spuds/SMF-ILA is a killer combo

It looks nice, indeed... you should add to it only the imageresizer/optimization option :-D

BTW, it has something to prevent uploading files > certain file size?

Sure, if you've that in the attachment settings.