Hi ya Ben
Most of your questions have bheen answered and I cannot add much to them. Congratulations on the scope, and I hope you have a lot of enjoyment with it. Alex (mental4astro) makes a good point about training your eye. Also try to learn how to judge seeing conditions. One thing I try to do is have a few targets that are large and bright that I look at all the time such as M42, Tarantula, Omega Cent and 47Tuc. That way I get a pretty good feel for how they look in good, average and poor conditions. I can then temper my observing to match. In realy good conditions a 4" will pick up quite faint objects and reveal lots of details even in target like M104, but will struggle in poor seeing.
As regards cameras, Canons have proven popular, I am not really sure why, I know there are some successful Nikon imagers out there, but Canon seems to prevail. Several people have used the 1000d quite successfully. Often times the features that you pay for in a High End DSLR are not really useful for astro work anyway, so a pretty basic camera does the job.
I am far from an expert re imaging! However I can make a couple of points. These samll scope are not really designed to have heavy cameras hung from them, the motors struggle and can slip and ruin shots. If you have a Neximage, play around with that for a while getting moon shots and planets and some of the brighter open clusters to see if you really enjoy imaging before spending a lot of $$$. Also beware! daring to dream is fine but really successful astro imaging is very expensive
!!!
Malcolm