Do I need a finer stone to use after the norton 8k
No but you will need a Crox pasted strop, to smooth out that edge a little. Shaving from the norton 8K is pretty common. It also means in the future you have a nice platform to go onto something that can further refine your edge. Be that a 10-12K hone, Or something more natural like a coticule, Jnat, Trans Arkie. Not everyone bothers with a finishing stone, and provided you get a good edge on the 8K then strop you might find you never want one.

The 4/8 would also put a good edge on the knives you mentioned. And a Crox stropping afterwards never goes amis.

Once you have the stone and the strop then you should be pretty much setup for any razor that doesn't need a full bevel reset. If you have to reset a bevel then your going to either have to work very slowly on the 4K or grab a 1K.