Lots of cronjobs at once?

depends on what exactly those cronjobs do.
if they are heavy tasks it will just delay the process and make the server slow at those times, you could split then in a small interval, and it would be alright.

Yup, if you give all your cronjobs the exact same start time, they'll all be started at once at that time.

It's usually a good idea to spread your cron jobs out over time, especially if any of them are going to do anything especially CPU/disk/database intensive. Running lots of tasks at the same time that all require the same resource will generally result in a longer run time than if you ran all the same jobs sequentially, due to task switching, disk head seeking, etc.

Another option to consider would be writing a simble bash script that will run your jobs in sequence, then just run the script from cron. Call it "nightlymaintenance.sh" or something. This can make for easier management as well, since you can just update the script, instead of adding a cron job every time you add a task.

Dan.

I would never recommend running them all at the same time, no matter what they are.

I've shut down servers with too many cron jobs, stagger them out like 5 minutes apart, and dear god be on a dedicated server (like those at OC3Networks )

Good answers