Inc Wire diameter, inc spring weight
Inc Spring diameter, decrease spring weight
Inc no. coils, decrease spring weight
With a linear rate spring, preloading does not alter the spring weight, 1st inch of travel has same weight as second inch of travel
With a progressive weight spring, preloading can greatly affect the rate, usually progressive springs have different spacing on coils so that as they compress, narrower spaced coils become coilbound and thus are taken out of the spring - fewer coils = increased spring weight. Sometimes, the coils change outer diameter also - seem this on koni coliovers.
Springs is a trial and error thing and largely down to personal preference - and the best is the softest spring that will do the job, soft spring=tyre on road=good thing. The main handling characteristic of the car comes from spring rates F/R and ARB's are supposed to be only for fune tuning this inherent balance.
You ideally want a spring that will have your car with level wishbones on average for the most time at a given track - this is the point of optimum geometry, least geometry change for a given amount of suspension movement, and thus most grip. For a FWD car, best bet is to set this for the front first and then fine tune the back to give a handling that you like to match the front. On a hatchback, because of the crap design, the arb's play a big part in this as to stop roll, the spring would have to to too hard to soak up the bumps. On a proper race car, they rarely have arbs.
Good luck.