We travel alot to visit family and luckily this has included many trips to WDW. We try and handle behavior situations just as we would at home - no more or less strict and the expectations are about the same. Granted there are later nights and more opportunites for melt down - but we handle them in our usual manner. Let me try and address your specific questions -
Souviniers - My personal feeling is that if my girls have saved their own money then I don't monitor what or when they buy. I will of course give them advice but ultimately leave the decision to them. They have already learned the lesson of buying "junk" at the drug store only to have it break, they had to learn it for themselves, KWIM? I am not sure I understand what your reluctance is on when they buy unless you don't want to tote it around all day? If your staying on-site, purchases can be shipped back to the resort. If not then our rule would be you want it now then you are responsible for carrying it all day.
Height restrictions - at 8 and 10 I don't think this is going to be an issue, the highest restriction at the theme parks is 48" although Disney Quest has a couple 51" restrictions. I think there is a section here on the dis with specific info. If one child wants to ride and the other dosen't or isn't tall enough ask about "child swap" so both adults can ride without waiting the line twice.
Morning routine - hate to be redundant, but we handle this just like at home. Set a time in the evening befpre that you would like to be out of the room the following morning and make that the goal.
Bed time - this is where we differ the most from what we do at home LOL. We often close a park at WDW and by the time we arrive at the hotel no one has a problem going to sleep. I do allow some tv while laying in bed as its often hard for my girls to wind down after such an overstimulated day.
Hope this helps - have a great trip.
TJ