full coilover kit = spring and shock combo

coilovers and springs each have their pro's and con's. if you get coilovers, you can adjust the your ride height until your happy with it. with springs, you'd be pretty much set. there are a lot of knockoff coilovers out there, thats why i prefer name brand springs (H&R, eibach, neuspeed, etc)

i doubt that coilovers will slip (if installed correctly, but thats why i prefer springs also)

i think the only reason why people get different brand springs is because each lowers different. some will be 1.75, some will be 1.5, etc. just get a set with the desired number of inches you wanna lower.

and yes, if you get a good set of aftermarket shocks, i think u'd have a good ride with any set of springs/coilovers. if you want an even better ride (at any height), get the full coilover kit.