Erm...Kakashi has the mangekyou, to say his sharingan is limited since the transplant is a tad silly considering he has activated the sharingans "true power" is quite a feat if hes a 2nd rate sharingan user.
In fact hes the first non uchiha to recieve mangekyou, and the 4th overall (madara and his brother, then itachi, then kakashi, then sasuke)
It has been stated by sasuke and itachi that kakashi can use his sharingan as good as an uchiha-but he gets worn out easily because he does not have an uchiha body.
Uchihas have high chakra capacities, sasuke as a genin had 2 chidori shots, kakashi said he only had 3, and he was an elite jounin and a ex ANBU member.
The reason kakashi cannot copy FRS is because it requires either
a)a brain that can look left and right at the same time, in other words a bigger genius even than kakashi or shikamaru
b)shadow clones all putting chakra into the jutsu
Kakashi has nowhere near the chakra supply naruto has, if kakashi ever did manage FRS it would use 90%+ of his chakra capacity, FRS is an amazingly powerful jutsu that only naruto is capable of.
Sharingan can copy anything as long as it ISNT
a)a KG
b)An element they dont have (surely the kakuzu arc showed clearly no ninja can use 5 elements, and kakashi MANGA wise only has 3, water, earth and electricity, fire was added in the anime, which is not the true story)
c)beyond the users chakra control, this is my point about byakagun with hinata vs sakura.
The sharingan can see the chakra control, but as lee said, if you cant keep up, theres no use in seeing it.
Seeing it and using it are two different things, and if you cant keep up, who cares?
d)beyond chakra capacity.
The sharingan does have limits certainly, it is also possible to beat a mangekyou sharingan now despite it being said you cant for 390+ chapters, oh well.