mother selction and cloning.

so i could use a little advice.. i hate to always be asking but i would rather that than do it wrong..

anyway ive got a 6ft by 6 ft grow tent.. and 4 600watt lights in there..
ill be growing 36 plants. one per square foot..
18 big bud and 18 AK48

but i would like to optimise my grow by selecting the biggest and best mothers for each strain.

so i have now 15big bud (sensi) and 15 Ak 48 (nirvana)
if you were me now and you wanted to find a great mother from each .. how would you go about it?

my plan was to grow all 30 ..
grow them out untill i can clone them then take 2 clones from each .. (just incase one clone doesnt make it)

flower the original 30
then i can destry the males and their corrisponding clones...
then wait it out and see which ones give the best results and by that time the clones i took will have been topped and trained to be good mothers in which i can take clones for a new batch.

only problem is i will need a lot of clones... 36 but then i will have to account for ones that dont make it .. so what like 50? so i can selct the best 36 to grow..

but im a little confused as to how many mothers i will need to cover 50 clones for the first run.

if i know i can build an area for the mothers now..

no-one had experiance doing something similar?