GIMP :: Crop Photos / Saving Stuff To PNG

I'm starting to get serious about photography. I've shot a batch of photos that need manual processing. There are a couple of steps where I should be able to save one or two keystrokes every time. This may sound minor, but when I have to do it time after time after time, it gets annoying. This is not intended to be a rant, but rather a request for info about changing defaults to speed things up for me.

I'm running Gimp 2.6.11 on Gentoo linux (64-bit). I've looked at "Edit ==> Preferences", but can't seem to find what I'm looking for there.

1) I need to crop photos, but the manual "crop tool" is not the best fit. I prefer to use "Image ==> Canvas Size". My problem is that the Width+Height aspect ratio defaults to staying constant. I.e. if I crop the X size, the Y size changes proportionally. I do NOT want that. I have to manually click on the link to break the linkage. Sometimes I forget, which can get really annoying, when cropping in one dimension crops the other as well. How can I change the default to not link the X+Y sizes?

2) Saving stuff to PNG
*) After having done any cropping, I obviously want to save my work. Saving to PNG pops up a dialog about "Your image should be exported before it can be saved... Is there any way to get the PNG save routine to just do it, rather than popping up a dialogue?

*) If I'm saving to a new PNG file, I get YET ANOTHER DIALOGUE with settings for compression/interlacing/etc/etc. I never change the default settings, so this is another extra annoyance to me. How can I get the "save as" command to "just do it"?