Yes, Apple iPhone 8 does have the OIS. It helps greatly with blur in the event of shaking hands or dim lighting and the larger sensor consistently picked up more light for better low-light photos.
Yes, iPhone 8 does support fast charging.
iPhone 8 does support fast charging. Apple iPhone fast charges up to 50 percent in 30 minutes when you use an Apple USB-C to Lightning cable and one of these adapters: Apple 29W, 61W, or 87W USB-C Power Adapter.
Yes, you can record 4K videos with iPhone 8.
You will get about 51-52GB as free memory in case of iPhone 8 64GB. However, this is very much dependent on the software version.
No longer the gold standard, the iPhone 8 is still all the phone you need.