aaaargh we could do with a sticky thread giving a list of suspension options and a quick brief on the different ones....
every car is going to feel different, depending on what other parts are fitted. it will be really difficult to compare a car with Koni FSD's and standard, old bushes(wishbones, roll bar for example, but not worn out bushes) to a car with Koni Sports and new bushes. there are som many different things that affect the way a the car will behave.
even the cheapest option like a front upper strut brace will change the cars behaviour for the better. front upper and lower braces can be had for £100ish.
i have the Koni Sports on my 2.0 TS 156, i also have Eibach's roll bar (F&R) and poly bush kit, front upper and lower strut braces, new front wishbones(upper and lower) new droplinks (front and rear), new trailing and transverse arms. i couldnt give you a true comparison unless someone had exactly the same upgrades done at roughly the same time, but had the Koni FSD's fitted instead.
to answer your questions,
1) yes, the koni & eibach combo will be a bit harder, but not teeth-crashingly hard. both the Koni Sports and FSD's have adjustable damping, so can go quite soft if you wish, although this setup will not be *optimum*
2)best to get them done at the same time if you are going to, as the shocks/spring need at least moving to fit the wishbones.
3)FSD's are more expensive because they are ride height&damping adjustable, whereas the Sports are fixed height (-35mm i think) but have adjustable damping (damping=soft/hard). FSD's may be slightly harder, but again the ride depends on the car's setup, bushes/wear etc.
hope this helps a wee bit.