Lagos is bigger than New York, so its literally always popping.
Street food comes in all shapes and sizes - MAMA Put is literally street food prepared by old women, They serve them in small canteens in many roadside restaurants. While if you find a good one they can be excellent and cheap, but i wouldn't recommend this as an new visitor. Thankfully Lagos has numerous amazing restaurants and eateries of all types for you to choose from. Excellent african eateries like Mama Kass, Mr Biggs, and Tantalizer are all excellent Nigerian fast food retaurants. If your head to VI or Ikoyi, there are plenty of high end restaruants of all ethnicities.
Real street food I would recommend Suya. These are served in by mant roadside street vendors.
The key with street food is hygeine. As long as the food is HOT, you should be fine. Eating cold street food is defintely a no no and a great way to get food poisoning.
Youth culture is very vibrant. Youth outnumber the old by a significant margin in Nigeria, so manyt youth centered movements are alive and well. Especially music, art, and fashion.
Nigeria is literally the home of Afrobeat, so there are literally HUNDREDS of Afrobeat artists based in Nigeria. Wizkid, Davido, PSquare, and Olamide are just of some of the huge Afrobeat megastars that call Lagos home. Lagos is also home to the "Fela Shrine" which is a MUST visit for any true afrobeat music fan. Thats located in Ikeja and is a MUST VISIT for any tourist. Consequently, the nightlife in Lagos is fukking AMAZING. The best afrobeat clubs are here and even strip clubs are fire. I can tell you these later if you're interested.
fukk learning Yorouba. Learn Pidgin English. That will take you much further in Lagos. Pidgin is quite easy to learn but takes a little practice. Consider watching Nigerian movies on youtube to get a grasp on the language.
Lots of malls in Lagos, but fukk em. They're overpriced usually. Shoprite is the big shopping mall chain in lagos, but high end boutiques and open air markets are the best way to shop. I recommend Lekki for the best shopping personally. The art market in Lekki has amazing pieces for cheap.
As far as etiquette and cultural mannerisms - DONT BE FLASHY!! This is the easiest way to get targeted. Fancy watches, extremely expensive shoes, or clothing may have you the target of pickpocketers.
Smiling and having an agreeable personality will take you far. Nigerians love money so tipping will take you far as well, but don't over do it.
Crime in Lagos is high. Remember, its like a big metropolis. Think New York but bigger. Like any big city watch your back and move accordingly.
AA would be gucci. I would recommend going if you're interested. Going with a Nigerian or tour groups may be ideal to get around more efficiently though.