See in the picture, with that 64mb card at 4k you'll get 2 hours at 1080p you'll get longer, the batteries last about 30 to 40 mins, new batteries last longer
Yes, you can power it by the charging cable from the bike but you need to get a diiferent battery comartment cover or the cable and battery are exposed.
Suptig Upgraded Battery Door Cover, Replacement Side Door for GoPro Hero 13, 12, 11, 10, 9, Water Snow Resistant IPX 6 Waterproof https://amzn.eu/d/0dB3GNYh
Not sure if the 8 door is different, you’d need to check.