Its as safe as the two separate, and quite pleasurable. Speed, is not safe though. Its very rough on your liver/kidneys.
It's safe. It might make your heartbeat that much faster, but you should be fine. If anything it will decrease the negative side effects of the ritalin. From my experience with mj and adderall the cannabis made me less uptight and allowed me to actually eat something. I've never had a panic attack with cannabis, but some people have in which case consuming both would only make the situation worse. Good luck.
It's really really weird. The only real difference is the weed will balance out your medication, so you'll be talking more than normal. Haha, one time I did it and it was freaking my friends out because I was more active than they were, but still blazed. Man, those were the days. Now they're always so damn busy...
safe. I would suggest not drinking lots of alcohol if you were going to be worried about mixing your meds with fun stuff.