You get 11 contact hours a week in first year: three two-hour seminars, three one-hour lectures, and a two-hour workshop. They do tend to spread them out so you're in class at least once a day, every day. They expect 100% attendance as you can expect, but I think dropping below 80% is when they actually start to call you out on it, and below 50% when they really chase you down. To be honest, it's your degree so if you need to miss the odd lecture or seminar (lecture attendance isn't recorded) they won't mind, but you won't want to miss too much or you'll lag behind surprisingly fast.
The accommodation varies a LOT, from the ridiculously nice to (if I'm being honest, here) the surprisingly subpar. It depends entirely on what you get: Northfield, Lewes Court and Stanmer Court are all quite nice, whereas Park Village (where I was) and East Slope are very small and minimal.
The course is fantastic. You don't get any choice in first year as to what you study, but after that there are loads of modules to choose from, and so many non-English elective modules to study instead if you don't fancy any of them. It's almost entirely coursework based, apart from two pretty gnarly three-hour exams per year, so you've got more control over your assessments. Word of warning though, the Critical Approaches module in first year is absolutely amazing and incredibly interesting, but very hard at times, so if you come to Sussex get a headstart on your theorists/philosophers ASAP!
The nightlife is very good in Brighton as well, because while it doesn't have as many huge tacky clubs as places like Birmingham, there is *so much* in town for all interests and types, I'm still finding new stuff and I've been here bloody ages. Standard modern clubs, retro places, Hawaiian styled places, more pubs and bars than you can count, loads of LGBTQ places (probably the most you'll find in one place anywhere in the UK), seafront places, indie places, live music places, literally everything. And if you don't fancy the bus ride into town, East Slope and Falmer Bar on campus are definitely worth spending a chill evening at. Plus, there's a student night pretty much every night somewhere in town. The night life will definitely not disappoint.
There are a lot of societies, although I personally never really got involved in anything much outside of Live Music. They're super friendly and enthusiastic to get Freshers on board though, and the Freshers Fair at the beginning of the year (a fair where all the societies come out and make themselves known, basically) is always extremely popular.
Making friends depends entirely on your own circumstances. I was extremely anti-social when I first came to uni, but because I ended up in a sociable house, I changed my ways and ended up going out two-three times a week (English is relatively lightweight as far as workloads go). I can't really comment on how easy it is to make friends because everyone's experience is different, but I will say that there is a million ways to make friends at uni, so don't worry about it! I love it at Sussex, especially because it made me a million times more sociable.