starting to build my own sound system

hi guys im thinking to start to build a custom sound system for dub,steppas and need some advise

my idea is to build a 4 way system with
four 21 inch sub scoop bins
two 21 inch kick scoop bins
four 18 inch mid high horns
and two times 4 tweeter boxes (Icosagonal)

i would like to run with a custom built pre amp with internal crosover and 10 band graphic eq (ENFORCER JTS or dubsonic dub master)

but i would like to have the design clear before buying any components

my question is i cant find plans for a 20 inch super scooper for the 4 subs and 2 kick bins
and not sure what the best design is for the four 18 inch horns

and when it comes to buying drivers and amps i am completely lost as their are so many

am i going in the right direction

thanks in advance

looking for some thing like the picture

one word, ok a few, 21" high bass and 18" mid high, sorry this will sound bad..... the transient response of a 21 makes it too slow for anything over 120hz, and the same with an 18" for mid high....

Stick to a 15" for high bass and a 12" for the mid high..... for me 18's as high bass and even kick just sound so slow..... unless you want to spend big big money on very high quality drivers, that still will only sound ok.... but defo not an 18" for midtop....

Also scoop on scoop for high bass is another bad idea (re picture) the top scoop will cancel out.