Hello! Depending on where your passport is from, you may not need a visa for a visit under 30 days, consult here (US and Canada are not on the list)
Apps you may need are WeChat and/or AliPay, and for a VPN to be able to onto the liberal website "Hexbear" I use Mullvad.
Early October isn't exactly the best time to visit if you're going during the start, as it's 八一 which means there will be a lot of domestic tourists. A lot of locations/trains will be absolutely flooded or booked out. In later October, the South will still be t-shirt and short weather while the north will be colder, meaning you should pack some jackets (I'd recommend layers to easily put on take off as needed)
The blue share bicycles are available for tourists (as they are AliPay) whereas the yellow Meituan ones are rented through WeChat and require a Chinese phone number (which requires a Visa/身份证 to obtain)
You'll also notice food portions get larger as you travel north. Always reminds me of my Tianjin grandfather saying something about southerners being stingy and/or greedy. If you ever hit the north east (东北)you might actually encounter all you can eat buffets for like $3 USD. Bear this in mind when you're ordering food, to avoid ordering too much once you get to the north.
Thumbnail: Chinese flag vs American flag
Actual content: Anything but Chinese
Result: Chinese
Lol