They should have an induction day - usually more than one, perhaps a three day run. This will help a lot.
My DS is going to his enormous new school this year too but fortunately he moved schools at the beginning of this year and it will be a great opportunity to meet up with all the friends he's missed since then from his last school, as well as those in his same peer group from this year.
I've explained to my DS that he will need a timetable and move classes to find the lessons, and that a map would be a very good idea and they should be issued in large schools. The first week they will all travel around together but by half term they should know their bit of the school blindfold, so need to pay attention to reference points etc.
I'm going to buy DS a school diary before he goes, there will be timetable info in there as well as other useful stuff.
Research transport opps, there may be a dedicated bus but if your child does an afterschool class they will need another way home - we have a choice as DS could feasibly cycle and also catch the public bus.
Cycling - go out on some Sundays and time the trip (essential), investigate short cuts etc.
Ref mobile phones - please, people, I grew up with NO electronic media at all bar perhaps an LCD watch ... Mobiles cause enormous issues at school - inappropriate use, envy, all sorts of nastiness. My DS has one so he can communicate with his dad, but that's all. He won't be taking it to school, in fact he said he'd be scared of someone taking it off him and breaking it if he did. If he was going to someone else's house after I might let him, or other relatively exceptional circs, but my kids have had the free roam of our village since age 7 and can take responsibility for their behaviour including coming home at the right time without needing a phone with them. And it's a very old phone. Very. With JRT tooth marks in.
One way to increase away from home confidence on public transport is to get together with some of the mums and arrange for some of the kids to go to the flicks as a gang by bus in the summer hols. They can all egg each other on to get the right one (teach them to read a bus time table first, these days they are not the krypton factor versions they used to be when I was a kid), and get on and off in the right place. Or the pool. Library. BK. Whatever.
I don't remember having difficulty with time tables and books on the right day etc, but I grew up with a certain amount of responsibility and a lot of self sufficiency and so have my kids so hopefully this won't be an issue.
There is still quite a bit of time to work up to this stuff, for anyone with kids not so confident.