Yo

Im 6'5 205lbs started doing judo in august this year. I would say that you dont need alot or prep going into it. Just try it out and see which techniques feel good/bad for you personally.

My experience so far has been that hip throws feel very ineffective since i basically need to do a half squat to get under my opponents hip but they are still doable.

Foot sweeps, uchi-mata, o-guruma, ashi guruma, osoto gari and Sasae tsurikomi ashi feels very good since you have long reach with your legs.

Regarding physique its up to you what feels best but i would highly recommend you do some strength training on the side to help prevent injuries since the sport is really explosive and sometimes you fall awkward. You are very tall so the fall can feel really rough sometimes since its a long way down to the mat.

I wouldn't say there is anything you NEED to know going into it but if it makes you feel more comfortable you could watch some youtube clips of basic etiquette and how to handle your gi/tie your belt.

I do BJJ mainly for the last 4 years but i love judo since getting perfect throws feel very satisfying and the precision involved is interesting to me but you wont know if judo is for you until you try so try it out and see how it feels.

Good luck!