24fps won't be blocky as such, it will look great on a pal tv if done in a cinematic style. if you want it for YouTube then 60fps is the way to go. Any higher you only need if you want to shoot slow motion. Downside with this is your editing time goes through roof so I normally use 1080 60fps
You have a few options but the best is shoot with 4k and crop down to 1080 (If you don't have a 4k device to view on), that is what the pros do that chop down to 1080 as the pixel count and quality goes up versus normal 1080 shooting mode.
The hero 4 doesn't have gyro stabilisation but you can get a brushless gimbal from about 150 quid, that is a game changer. If you look at my YouTube channel you will see videos recently with gimbal and older ones without, there is a noticeable difference but up to you if you think it is worth doing. Camera Gyro stabilisation is decent but it absolutely hammers quality as it basically only uses the centre of the sensor for picture and uses the outside to pixel shift to give the impression of stabilisation, if you look at below video on the yellow rib, pay attention to the sky and you can see pixel shifting.
Go pro software I'm not a fan of but it works well enough. If you want software for editing then there is a vast array out there, I use Adobe premier elements which is fine for my basic nčeds.
I should add the above is a general action camera thing, whilst I own a hero 3 I never use it as I do all my recording on a gitup action camera. (Basically a hero4/5)
The video below are the same cameras, mines has gyro stabilisation off and in a brushless grip, the other has it on and handheld, you can see the difference even though both cameras have same settings.
P.S YouTube compression is a quality killer but thems the breaks, vimeo is better for quality but not as nice to use. All videos have artificats (blocking) on youtube due to their compression