I thank you for persevering and thank you for your nice post.
Answer to your first question:
You can install the new version right on top of old version and all your settings will be preserved, no worries.
(ps. you can also backup your settings for emergencies, it's a file called ScreenshotCaptor.ini -- stored in your mydocuments folder on win vista/7/8, or in ScreenshotCaptor directory on xp).
Answer to your second question:
You can tell SC to save all files as jpg files by default (see the Image File Format tab); you can experiment with the Compression Level to get the best file size vs quality tradeoff.
OR if you don't mind an extra step, you can capture in the normal PNG lossless format, and then just use SaveAs to save jpg when you need to post to your forum.
Answer to your third question:
For the fastest workflow -- I turn off the post-capture dialog, so you can just capture images without intervention. If you are posting on a forum, a really nice feature is go to the Post-Capture options dialog, and tell SC to capture the file PATH to the clipboard after every capture. Then you can capture an image and it will put the path on the clipboard where you can paste it into the file browse dialog that will be shown when you tell your forum to attach an image file.
ps. I'm going to move this post to the Screenshot Captor area of our forum.