im no expert but heres my opinion
alclad does not need thinning.. i use it the way as is.
ffw is thin enough to spray thru your airbrush and i do that when i want to coat either alclad or make something shine. i also apply it on smaller areas w a good brush.
createx paints are rubbery but i only use the pearlized ones. tamiya makes good transparents but they are thick. i use tamiya thinner for that.
as for the paints that dont need thinning i use vallejo and sometimes they dont need to be thinned and then theres some colors that do.