I have a video timeline that has about 300 stills... 2 questions
1. Is there any way I can change the duration of all events from 5 sec to 3 sec?
2. Is there any way to easily insert the same crossfade between each event?
If you haven't done anything yet besides drop them on the timeline, now is a great time to start over! Under options / preferences / editing, set the new still image length there to 3 seconds plus the length of crossfade you want, then set the cut to overlap conversion to the crossfade length. Now drag all the pictures to the timeline as one selected group and the duration & crossfade will be set for you.
If you're not at a point of starting over, select them all and press G to group them, then hold the Ctrl key down while you drag the end of the last image over to the left to speed them up. Then press the \ key to create crossfades between them (cut to overlap mentioned above sets the crossfade length).
With all the events still selected you can choose any other transition and drag it to to any crossfade and they'll all be set to that transition.
Tom my free Timeline Tools add-in for Vegas has an extensive collection of features for adding or removing Gaps, Overlaps and Fades. It can also set the Fade Type and adjust Event lengths for any Event already in the timeline. You can move one or more events around on the timeline or reverse the order of a selection of Events. You can also have the utility add a random transition effect to each Event.
These are just a few of the many features in the utility that are too numerous to mention.
You might want to use Quick Properties + Pan/Crop Assistant from Vegasaur toolkit (not free though). These tools have everything for working with a large number of events (especially in photo montages)