you can use red miso instead of white but as it is stronger I would use about 25-30g personally
you don't need to wrap it like i did - I just did it for photos. I actually just have a big old container of mixed butter in the fridge. If you do want to wrap it then use clingfilm to roll it into a log
miso butter keeps for 2 weeks in the fridge - supposedly!
start by adding 1/4 tsp cayenne in, taste and adjust. 1/2 a tsp is spicy but not overpowering - in my opinion