I've never done judo, but after speaking with and light sparing with a 2nd degree black belt in judo. I'd say be prepared to make the mat your best friend :S He told me that they throw each other so much you get to the point hitting the mat is normal. so there will be a great deal of conditioning involved, this way you can handle the riggers of judo and hitting the ground so much. you'll probably start with learning to fall so you don't get hurt when your thrown... my friend said he couldn't throw me throw, with out showing me how to fall, least I get injured but don't let that scare you off, he was a black belt and I don't do judo.
my 2 cents now we'll let an actual judo practitioner speak
What I know about judo (very little with few classes of it when I was a small boy) is that is the gentelmen martial art or the martial art of the gentle way, however, falling to the mat can be harsh and in some cases harmfull that's why the judoka spents most of his time doing break falls,rolls,etc. to get used to the pounding minimizing injuries. A good judoka can redirect the energy of the fall and stand up without any disconfort.
Besides the falls judo is a veru physical work out, demands a lot of stamina.
I do judo since 2011 and i love it
I suggest you focus more on landing techniques ( Ukemi waza) before you rush to learn judo throwing techniques.
Be sure that you will feel the positive result of this action in the future
First I would say invest in a quality gi that fits properly. An oversized gi is not what you want, it gives your opponent too much to work with material wise. The longer people are in judo, the tighter their Gi's get. Don't get silly with it, but definitely avoid an oversized, super loose fitting gi.
My technical advice would be to not worry about winning, or throwing your opponent. Focus instead on perfecting your posture and movement. Perfecting your posture is one of the keys to success at throwing and defense.
To much focus is spent on breaking your opponents posture and balance, without first perfecting yours first.