I guess it's ok, sort of. Does your motor really only draw 8mA?
Why do you have 2 caps in series? and why are they 10F!
The diode must be a schottky for only 0.3V drop. This is ok if you choose a big one like 1N5817 et. al. But, only at room temperature and at low current (like 8mA). If it gets hot it will drop more voltage.
Why not just use a linear voltage regulator, where most of the details have been done for you. You'll get better performance with fewer parts. For example 78L33, they cost about $0.50.
For the power rating, as it is now you should just take those caps as short circuit since to charge them to 3V will take quite a time. 12V through 1kOhm => you should be able to calculate the power and the current through the (serial) diode too.
Is this some kind of homework? For a real life problem this is just too ... special.
+1 @Vossi -- Your thread (well, actually your 2 threads, since you multiple posted it) is locked for Moderation. Please send me a Personal Message (PM -- click on my avatar and "Start a conversation") to let me know if this is for schoolwork or not. Thank you.