With clen you need to start low and slow and work up to a dose that feels comfortable. Also note that the long half life means that even with a fixed dose, the serum levels of the drug will continue to build over time. If you get in trouble with clen, the long halflife means that you will be a mess for a couple of days after you stop taking it.
As you will work upto and find a comfortable dose level for your body, if your caffine intake is constant, then that should work out ok. And if you feel overstimulated, you can reduce or stop the caffeine and its effect will wash out faster than the clen.
Clen can hurt you real bad, a lot more than anything else you are doing. The potential for harm is there. So start slow. And for future cycles of clen, start low again and do not start suddenly on the dose that you worked up to before.
As for the harmful effects of clen, T3 and caffeine are synergistic and have the ability to increase problems as well as effect. The big problem would be a racing and pounding heartbeat that simply will not stop. Never mix with ephedrine or stimulating rec drugs.
Clen use is also associated with dehydration and deplete potassium levels. So drink more water and eat some bananas. Don’t confuse weight loss with dehydration.