I use what is referred to as a 1:2:2 refresh. 1 part starter, 2 parts water, 2 parts flour. I do 50g starter, 100g water, 100g flour. If I keep 50g out for the next feeding, I have 200g to use to bake. I rarely need more than that.
Honestly, it doesn't matter nearly as much to get it going as most people make it out to be. Just feed it twice a day with a 50/50 flour water mix and you will eventually have a solid starter.
I wouldn't use it after day 4. I almost guarantee that you will be disappointed. I wouldn't use it until it consistently doubles in size. It's not going to raise bread until that happens. If it won't raise itself, it won't raise a loaf.