The most important effect is the fact that, running tires you and you will not be able to effectively workout. All your energy would have been spent in running and you wont have enough energy to workout with heavy weights.
Yes, in moderation
decreased flexibility
No. Running before your weight training routine can exhaust you of all your energy and you may not be able to workout to your fullest capabilities. If you want to run, then you can push the running to past the weight training workout. This way you can both workout in best form and run.
you should stretch your legs and arms for warming up
Running outfits are good for gyms as well if you're doing cardio or running.
Why do people stretch before and after running? Running is a tough and vigorous body workout. A lot of injuries can be caused by failure to stretch before and after running. More importantly, it is necessary to stretch to make sure that your muscles return to their normal shape or lengthen if necessary. -http: //whydopeople.net/why-do-people-stretch/
The type of sand you run on influences the difficulty of the workout -- if you are a beginner, you should run on damper sand, but if you have more experience or if that is too easy for you, run on looser, dry sand for a better workout.
Cardio classes can not only be as effective as running in terms of a workout, but better for you. They can be lower-impact and still get your heart rate up and build endurance.
Its better after a workout but you can before also.
Mizuno makes running shoes, so if you consider running a workout, then yes. They are not designed to be worn in a gym, but they are made specifically for runners.
If you are going to be running, it is a good thing to stretch, but more importantly than stretching before you workout is stretching after to get the ketones out of your muscles and prevent exhaustion.
It mean after your workout; not before or during, but right after.