Not sure that for the things that you mentioned that they are any good warning signs. A flash flood is something that can happen fast and in some areas can happen when it isn't raining where you are. Good examples of this are slot canyons. Be things to for this is watch the weather reports and if in a dangerous area if any where near is having possible storms go elsewhere. Rock slide there is no way to predict. At best if climbing or hiking on a trail in the mountains with loose rock don't walk directly under some one at higher elevation.
From these questions I take it you are new to backpacking or outdoor adventures. I see lots questions from newbies to backpacking/hiking. Here is some advice and how I learned. First thing is yes it is great to be prepared. However you can never predict everything situation you encounter so stop worrying so much. If you are unable to do that then don't go. Here is something to think about. Yes there are risk in any adventure that takes you off the beaten path. Here is what you have to decide. "Am I willing to take these risk?" If not stay home. That being said remember that there are risk with everything you do in life. One of the most dangerous things you can do is get in your car. More people get killed in cars then mauled by bears, killed by rock slide, or, even jumping out of an airplane.
So what I would tell people is not to over analyze things and get out and enjoy. Yes use common sense but don't think this is rocket science as it isn't. In a nut shell here is what backpacking is. You gather up all the crap you need. Add another 4 pounds of crap you think you might need, then add another pound or 2 of crap that we will never need but take anyway. Stuff it all into a pack and strap it to your back. Pick a trail and start walking. Walk until you want to stop, camp for the night and repeat process in the morning. Multiple day trips just carry more crap and repeat process multiple times. Other than that use common sense in what clothing in regards to the weather, and the same for sleeping bag selection.
In short relax if you want to experience this then do it. If nothing else hike a mile in or less from your car. Then set up cam and see if you like it and of your gear is working. That way if not you can leave easily.