It is a good idea to continue with the breeder feed at least for a while. Most breeders will give you enough to last a week to two so you can transition to a new feed. If you know what they have feed and can easily get that, you can continue with that food if you would like. If you would like to switch to something else, then do it slowly and mix the old and new foods.
For the litter box, you can just put it in the cage and hope the use it. You could also wait and see where the rabbit will pee and poop and put the litter box there. It can still take some time for the rabbit to litter train.
You should be able to handle your rabbit when you get it, but don't do too much too soon. You generally don't want to do too much for the first couple days so they rabbit can adjust and get used to the new environment. Each rabbit is different and some may want more attention right away than others. If the rabbit is shy and wanting to hide, then leave it to settle in before doing too much. If the rabbit adjusts well and is wanting to explore, then you can do more right away, just don't overwhelm the rabbit.