welcome.
theres alot of info on this site about buying a skyline and the checks to do.
so, to try and answer your question....
a) yes. they can be a good introduction to skyline.
but, what do you want eventually?
you may as well buy the car you want to own eventually.
b) in regards to price, the neater the car, generally, the more you will pay.
have a look around and get a good idea of what most are going for, then progress from there.
c) maintenance, how much do you expect to drive it?
I know you have stated as a weekend car, but mine is, and Im lucky to do 100-200kms a month.
you may do that every weekend.
general maintenance shouldn't be too much more then every other car.
d) sites to look at are the for sale, whole cars on this site.
ebay.
gumtreee.
carsales.
again look at as many as you can, and get a good grasp for price.
e) cant help here sorry, as im in nsw, but hopefully a vic person can chime in with some experience.
either way good luck with your hunt.
and be sure to post pics when/if you buy one.
in the meantime, post pics of your current ride, as we love all cars here, not just skylines.